Automated cartridge system

ABSTRACT

A storage and retrieval subsystem in a data processing system includes a plurality of magnetic tape cartridges, a host computer, and a library storage module storing the plurality of magnetic tape cartridges in substantially upright positions. The library storage module includes a first cylindrical array of storage cells centered about a vertical axis, a second cylindrical array concentrically arranged about the first array, and a library tape unit including a plurality of tape drives, each of the tape drives being adapted to receive one of the magnetic tape cartridges in a substantially horizontal transducing position. A robot within the library storage module is used to transfer selected ones of the magnetic tape cartridges between their substantially upright positions and the substantially horizontal transducing positions at a selected tape drive. A first controller outboard the channel communicating with the host computer is adapted to receive commands from the host computer for interfacing between the host computer and the library storage module, and a second controller inboard of the channel is adapted to receive commands from the outboard controller for interfacing between the outboard controller and the robot.

BACKGROUND OF THE INVENTION

This invention relates generally to data storage and retrieval, and moreparticularly to an improved method and apparatus for storing andretrieving large amounts of data contained in magnetic tape cartridges.

There exists a need in the marketplace, since the advent of computerssuch as the IBM 360/370, to store large amounts of data (e.g., in excessof 1 trillion bits) while consuming as little floor space as possible,and at the same time making the data readily available. Basically, twochoices for data storage have existed: (1) online, usually direct accessstorage devices (DASD), which provides fast initial service time throughsequential or direct processing; or (2) offline, usually manual 9- or18-track magnetic tapes, which provides a low unit cost per unitstorage. There exists a need, however, for many new applications werecostly DASD are not justified but where manual tape systems areconsidered too slow or too inconsistent.

One early approach, used in the IBM 3850 Mass Storage System, consistsof an array of data cartridges about 1.9 inches in diameter and 3.5inches long, with a capacity of 50 million characters each. Eachcartridge contains magnetic tape 2.7 inches wide and 64 feet long, onwhich data is organized in cylinders analogous to those of a disk fileand can be transferred to the disk file one cylinder at a time. Up to4700 cartridges can be stored in hexagonal compartments in ahoneycomb-like apparatus that includes mechanisms for fetchingcartridges from the compartments, for the reading and writing of data onthem, and for the replacement of cartridges in the compartments. Thefetching and replacing mechanism, however, is adapted to store andretrieve the cartridges from a linear rack. Accordingly, if a desiredcartridge is located remotely from the retrieving mechanism at one endof the rack, the retrieving mechanism would be required to move to theend, retrieve the cartridge, and load it upon a drive. It is, therefore,apparent that if a subsequently selected cartridge is located at theother end of the rack, much wasted time would be utilized in themovement of the retriever mechanism between opposite ends of the rack.

Various other tape library systems, have been devised for the storageand handling of magnetic tape reels. More sophisticated systems whichhave been used in the past, commonly referred to as automated tapelibrary systems, permit storage and automatic retrieval of datacontained on tape reels such as the conventional IBM 3420 tapesubsystems. As is well known, such tape subsystems provide a nominaldata rate of 1.25 megabytes per second, a recording density of 6250bytes per inch, and a storage capacity of 165 megabytes on 9-track, 1/2inch iron oxide magnetic tape wound about 101/2 inch reels. The tapereels, with tape supported by conventional vacuum columns, are loadedupon a drive system including a laminated magnetic head.

One prior art automated tape library system utilized for storing andretrieving data contained on such tape reels is disclosed in U.S. Pat.No. 3,920,195. The apparatus taught therein corresponds generally to theXytex Corporation XTL tape library which, under the control of an IBMoperating system, automatically brings tapes from storage positions oneither side of a linear rack, mounts them on tape drives, dismounts themwhen the job is completed, and returns each reel to storage. Averageaccess time for delivery of a single tape reel to a selected drive in amedium size system (accommodating up to 2.3 trillion bits of storage in3200 magnetic tape reels), however, is relatively slow. Such accesstimes include selector-positioning mechanism access, reel selection,access to the automatic mounting unit, and the mounting of the reel onthe tape drive (i.e., elapsed time from the operating system command tomount a tape to the time that the tape is physically mounted and readyto start the tape drive load cycle).

All reel storage matrices within the linear racks are serviced by thereel selector-positioning mechanism, which is part of the librarycontrol unit but which moves through each library storage unit on aconnecting rail. The selector-positioning mechanism selects and replacesreels from the library storage units through use of a segment whichrotates 180° for the selection and replacement of reels on each side ofthe linear library storage unit.

When a reel mount command is received by the library control unit, theselector-positioning mechanism is commanded to move to the address ofthe required reel in the array. After the selector-positioning mechanismreaches the addressed position, the reel is drawn from its storagelocation and the selector-positioning mechanism is then moved to theautomatic reel mounting unit which will service the particular tapedrive that the system indicates. When the selector-positioning mechanismreaches that location the reel is deposited in a pre-load position. Theautomatic reel mounting unit then transports the reel to the tape driveand mounts it.

The automatic reel mounting unit retracts within the storage unit whennot in use. There is a protective hood enclosing the drive hub of thetape drive which provides safety and security, and which can be pivotedout of the way by an operator to facilitate cleaning and servicing.Pivoting the hood automatically removes the drive from control of thesystem and makes it accessible for manual loading.

One particular drawback to the aforedescribed automatic tape librarysystem, however, resides in its linear storage configuration. Like theIBM 3850 Mass Storage System, the system described in U.S. Pat. No.3,920,195 suffers from certain access inefficiencies in cases where aselected tape reel is located at one end of the library, while the nextselected tape reel is stored at the other end. Moreover, while thestorage density per unit area of floor space taken up by the system isdoubled through use of a two-sided linear rack, large storage systemsincorporating more than one library storage unit merely aggravate theproblems of linear storage by extending the path through which theselector-positioning mechanism must go to transit from one end of thelibrary to the other.

Nevertheless, the use of standardized magnetic tape reels has been morerecently supplanted by small, rectangular cartridges such as those whichare used in the IBM 3480 tape subsystem. The rate at which data can bestored in the cartridge's one-half-inch wide chromium dioxide tape, orretrieved from it, is the result of using 18 recording tracks andachieving a linear data recording density of about 38 thousand bytes perinch (approximately six times the density used in typical tape reeldrives). Moreover, the four-by-five inch cartridge used in the IBM 3480tape subsystem is about one-fourth the size of a standard 10.5-inch reelof magnetic tape, yet it stores up to 20% more data, a total of 200million characters. The tape and cartridge requirements for the systemare as defined in the IBM document "Tape and Cartridge Requirements forthe IBM 3480 Magnetic Tape Drives", GA 32-0048-0, the contents of whichare incorporated herein by reference. Further details are disclosed inU.S. Pat. No. 4,426,047 and U.S. Pat. No. 4,383,660, and in the "SecondDraft, Proposed American National Standard, Unrecorded, Magnetic Tapeand Cartridge for Information Interchange" (ANSI-X 3 B 5/85-030,February 1985), each of which is incorporated herein by reference.

While the advances provided by the digital servo control and new headtechnology of the IBM 3480 Magnetic Tape Subsystem permit lowacceleration tape motion thereby eliminating the need for vacuumcolumns, capstans, and reflective markers have improved the level ofdata reliability as compared to conventional drives, the advantagesgained are nearly offset by the disadvantages accruing from the use ofbook shelf type storage racks such as those described in U.S. Pat. No.4,600,107. Furthermore, while the now-standardized IBM 3480 magnetictape cartridges improve such data reliability through reduction of bothcontaminants and handling damage, the storage and retrieval of suchcartridges must for the most part be carried out by human operators.Such human intervention not only degrades the reliability of selectionand replacement, but also prolongs the time from which a data request ismade and that data is read by loading a specific cartridge in anavailable tape drive. While recent improvements to systems utilizing theIBM 3480 cartridge which incorporate magazine type automatic loadershave reduced the time that jobs wait for cartridges to be mounted, suchsystems still require operator assistance and are inflexible as to themounting order once installed within the magazine. It would, therefore,be desirable to provide a storage and retrieval system for magnetic tapecartridges such as those of the IBM 3480 type which are capable ofstoring large amounts of data, while consuming as little floor space aspossible, and at the same time making the data readily available byminimizing human intervention.

Two such approaches used in the past are disclosed and claimed in U.S.Pat. No. 3,938,190 and U.S. Pat. No. 4,527,262. Unlike each of the abovedescribed storage and retrieval systems, the systems shown in U.S. Pat.No. 3,938,190 and U.S. Pat. No. 4,527,262 are both adapted for storinginformation-bearing units or modules in a polygonal configuration. Forexample, the storage and retrieval system for magnetic tape cassettesdescribed in U.S. Pat. No. 3,938,190 includes a fixed two-dimensionalstorage array, a fixed processing or play station for extractinginformation from the units, and a movable selection mechanism havingthree degrees of freedom for retrieving individual modules from thestorage area, transferring them to the processing area, and thenreturning them to the storage area after the information containedtherein has been extracted. Additionally, the system includes means forautomatically sequencing a series of units, as well as a preprocessingstation for cuing up individual units for intra-unit accessing.

The information storer and retriever shown in U.S. Pat. No. 4,527,262,on the other hand, includes a plurality of shelves disposed so as to besubstantially tangent to a cylinder of reference of a given diameterdefining an access corridor which is large enough to accommodate atransport apparatus in the approximate center of the corridor. Thetransport mechanism includes a carriage that is translatably disposed ona pair of parallel rods to effect X-axis translation of the carriagethrough the access corridor of the polygonal arrangement, and means forrotating the transport mechanism about the X-axis to select a particularshelf disposed within the polygonal arrangement. Once the appropriateangular position is achieved and the carriage has been translated in theappropriate distance along the X-axis, then the in and out movement orX-axis translation is ready for activation by appropriate means.

Each of the aforedescribed U.S. Pat. No. 3,938,190 and U.S. Pat. No.4,527,262 effectively stores and retrieves a plurality of informationbearing media, but both are limited in the amounts of discrete mediawhich may be contained therein. The substantially circular arraysprovided increase the amounts of data which may be stored per unit floorspace, but neither system includes the capability for expansion ofstorage by interconnecting individual storage units, one with the other,to improve data handling efficiency.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to providean improved method and apparatus for storing and retrieving largeamounts of information. More specifically, it is an object of thepresent invention to provide a storage and retrieval subsystem in a dataprocessing system having a host computer and a plurality of tapetransports coupled for communication with the host computer, each of thetape transports being adapted for use with magnetic tape cartridges.

Another object of the present invention is to provide an automatedcartridge system for storage and retrieval of magnetic tape cartridgesused in a data processing system, thereby minimizing the requirementsfor human intervention.

Still another object of the present invention is to provide an automatedcartridge system which stores the cartridges in a first position adaptedto prevent damage to the magnetic tape contained therein, and whichtransfers selected cartridges from their stored position to a second,transducing position upon the tape transports for reading data therefromor writing data thereto.

Yet another object of the present invention is to provide an automatedcartridge system which is capable of communicating with a plurality ofhost computers.

A further object of the present invention is to provide an automatedcartridge system which includes improved robotic means having aplurality of degrees of freedom for rapidly accessing a selectedmagnetic tape cartridge and loading it within a particular tapetransport.

Still a further object of the present invention is to provide animproved robotic means with redundant means for picking and placingindividual magnetic tape cartridges.

Yet a further object of the present invention is to provide an automatedcartridge system which is accessible for manual loading of magnetic tapecartridges, as well as the transference of a plurality of magnetic tapecartridges between discrete storage modules.

Another object of the present invention is to provide a method ofcontrolling the storage and retrieval of data which optimizes therobotics motion to maximize media handling performance.

Still another object of the present invention is to provide a method ofcontrolling the storage and retrieval of data from magnetic tapecartridges which is capable of interfacing a plurality of host computerswith a plurality of storage modules.

Yet another object of the present invention is to provide an automatedcartridge system which includes means for self-calibration andself-diagnosis.

A further object of the present invention is to provide a storage cellfor containing a magnetic tape cartridge in an automated cartridgesystem, the storage cell including a unique target which minimizes fineadjustments to the robotic means when used in conjunction with aconventional vision system.

Briefly, these and other objects of the present invention areaccomplished by a storage and retrieval subsystem in a data processingsystem, wherein the subsystem includes a plurality of magnetic typecartridges, a host computer, and library means for storing the pluralityof magnetic tape cartridges in substantially upright positions. Thelibrary means according to the invention includes a first cylindricalarray of storage cells centered about a vertical axis, a secondcylindrical array concentrically arranged about the first array, and alibrary tape unit including a plurality of tape drives, each of the tapedrives being adapted to receive one of the magnetic tape cartridges in asubstantially horizontal transducing position. Robotic means within thelibrary means is used to transfer selected ones of the magnetic tapecartridges between their substantially upright positions and thesubstantially horizontal transducing positions at a selected tape drive.First controller means outboard a channel communicating with the hostcomputer is adapted to receive commands from the host computer forinterfacing between the host computer and the library means, and secondcontroller means inboard of the channel is adapted to receive commandsfrom the outboard controller means for interfacing between the outboardcontroller means and the robotic means.

In accordance with one important aspect of the invention, the roboticmeans includes a six-motion, servo controlled mechanism for picking amagnetic tape cartridge selected by the host computer, transferring thatcartridge to an available tape drive, and loading the cartridge upon thetape drive in a transducing position for writing data thereto or readingdata therefrom.

In accordance with another important aspect of the invention, thelibrary means may comprise a plurality of storage modules, eachcomprising first and second cylindrical arrays, wherein the individualstorage modules are connected for transference of magnetic tapecartridges therebetween in order to modularize the library means andthereby provide the capability for add-on storage. The transferencemeans, according to the present invention, includes means for acceptingcartridges placed by the robotic means of one storage module in orderthat they may be picked by the robotic means of another interconnectedstorage module.

In accordance with still another important aspect of the invention, eachstorage module includes means for inputting and outputting cartridges bymanual means, while maintaining the automated capability of the roboticmeans. Such input/output means further comprises safety means forpreventing access to the interior portion of the storage module whilethe robotic means are in operation.

Other objects, advantages, and novel features of the present inventionwill become more apparent from the following detailed description of apreferred embodiment when considered in conjunction with theaccompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an automated cartridge system according to oneembodiment of the present invention;

FIG. 2 is a block diagram of an expanded ACS according to the presentinvention;

FIG. 3 illustrates in plan view, partially cut away, a library storagemodule with its associated tape drives and library control unit;

FIG. 4 illustrates in elevational view the library storage module andassociated tape units of FIG. 3 take along the lines IV--IV;

FIG. 5 is a sectional view of the harmonic drive means shown in FIG. 4,taken along the lines V--V, and a view partially cut away of a crashstop according to the present invention;

FIG. 6 illustrates the Z-mechanism and wrist assembly shown in FIG. 4taken along the lines VI--VI;

FIG. 7 illustrates in plan view the Z-mechanism and wrist assembly shownin FIG. 6 taken along the lines VII--VII;

FIG. 8 illustrates in sectional view one hand and finger assembly androll mechanism of the wrist assembly shown in FIG. 7 taken along thelines VIII--VIII;

FIG. 9 illustrates the hand and finger assembly of FIG. 8 at itsextended position;

FIG. 10 illustrates in sectional view the finger assembly of FIG. 8taken along the lines X--X;

FIG. 11 illustrates in front elevational view the hand and fingerassembly of FIG. 8 take along the lines XI--XI;

FIG. 12 illustrates the hand and finger assembly of FIG. 11 rotated 90°for storage of the magnetic tape cartridge;

FIG. 13 illustrates in plan view a carriage for loading the magnetictape cartridge in conjunction with the hand and finger assembly shown inFIG. 8;

FIG. 14 illustrates the carriage assembly of FIG. 13 in its unloadedposition;

FIG. 15 illustrates the carriage of FIG. 13 in its loaded position;

FIG. 16 is a block diagram of the tape transport shown in FIG. 4, aswell as its associated tape control unit;

FIG. 17 illustrates in plan view the access doors and cartridge accessport shown in FIG. 3;

FIG. 18 illustrates an elevation view, partially cut away, the cartridgeaccess port shown in FIG. 3 taken along the lines XVIII--XVIII;

FIG. 19 illustrates in sectional view the cartridge access port of FIG.18 taken along the lines XIX--XIX;

FIG. 20 illustrates the cartridge access port of FIG. 19 in its openedposition;

FIG. 21a illustrates in detail the pass through port shown in FIG. 3;

FIG. 21b illustrates another embodiment of the pass through port;

FIG. 21c illustrates in sectional view the pass through port shown inFIG. 21b;

FIG. 22 illustrates a storage cell for containing magnetic tapecartridges in accordance with the present invention.

FIG. 23 is a block diagram of a library management unit (LMU) accordingto the present invention;

FIG. 24 illustrates passage of data within a central processor module(CPM) of the LMU shown in FIG. 23;

FIGS. 25a and 25b illustrate paged memory mapping of the CPM shown inFIG. 24;

FIGS. 26a and 26b illustrates various external registers of the CPMshown in FIG. 24;

FIG. 27 is a block diagram of an interface processor according to thepresent invention;

FIG. 28 shows external registers used with the interface processor ofFIG. 27;

FIG. 29 illustrates interrupts used with the interface processor of FIG.27;

FIGS. 30a-30f illustrate details of the external registers shown in FIG.27;

FIG. 31 shows a block diagram of a serial time interrupt controlleraccording to the present invention;

FIG. 32 illustrates an IPM interface according to the present invention;

FIG. 33 shows an LMU operator's panel;

FIG. 34 illustrates transfer of data from a terminal control unit to theLMU;

FIG. 35 illustrates further transfer of data between the terminalcontrol unit and LMU;

FIGS. 36a-36d show MOUNT requests and responses with a flow chart of ACSactions;

FIGS. 37a and 37b show DISMOUNT requests and responses;

FIGS. 38a-38c show SWAP requests and responses with a flow chart of ACSactions;

FIGS. 39a-39c show MOVE requests and responses with a flow chart of ACSactions;

FIG. 40 shows a flow chart of ACS actions upon an ENTER command;

FIGS. 41a and 41b show CATALOG requests and responses;

FIG. 42 illustrates transmission and acknowledgment of an LMUcommunication;

FIGS. 43a-43e illustrate commands, responses, rejects and error messagesbetween the LMU and an LSM;

FIGS. 44a and 44b illustrate commands responses, rejects and errormessages associated with the cartridge access port;

FIG. 45 illustrates commands, responses, rejects, and error messagesassociated with the pass through port;

FIG. 46 illustrates LSM monitoring communications;

FIG. 47 describes control program interfaces to LMU tasks and hardware;

FIG. 48 shows input/output through LMU software;

FIG. 49 is a block diagram of LMU functional software;

FIG. 50 illustrates an exemplary process host request task;

FIG. 51 lists system calls used by the control program;

FIG. 52 shows a block diagram of LSM functional software architecture;and

FIGS. 53a-53c are block diagrams of LSM data flow.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, wherein like characters designate like orcorresponding parts throughout the several views, there is shown in FIG.1 an automated cartridge system (ACS) 100 according to one embodiment ofthe present invention. The ACS 100 is designed to operate with an IBM,or IBM-compatible host computer 102 capable of communication with aconventional 327X-type terminal controller 104 as will be described infurther detail herein below. Comprised generally of a library managementunit (LMU) 106 and a library storage module (LSM) 108, the ACS 100,through its associated host software component (HSC) 110, enablesstorage and retrieval of approximately 6000 magnetic tape cartridges ofthe IBM 3480-type for use by the host computer 102 across a conventionalchannel 112. Each LMU 106 serves as the library controller and providesthe interface between from one to sixteen host computers 102 and up to16 LSMs 108, as shown in FIG. 2. The LMU 106 thus acts as an outboardcontroller and interprets commands from the host computers 102, relayingappropriate instructions to the selected LSM 108 via a control path(shown in solid lines) and a library control unit (LCU) 109. On theother hand, the read/write data path (dashed lines) comes directly fromthe host computer 102, through a tape control unit 111 to the tapetransports 150 as will be described further herein below, therebyseparating control signals from data signals.

Each LSM 108 provides the necessary mechanisms for automated cartridgehandling. It not only provides the storage area for magnetic tapecartridges utilized in the system, but also includes an optical systemfor identifying the correct cartridge, a servo-controlled,electromechanical means of selecting the proper cartridge and deliveringit to the correct tape drive, and a suitable housing to ensure operatorsafety and data security. As shown in greater detail in FIG. 3, a LSM108 is comprised generally of an outer housing 113 which includes aplurality of wall segments 114 attached to floor plates 116 and disposedabout a vertical axis A. An inner wall 118 having a plurality ofsegments 120 forming an upper portion 122 which is suspended from aceiling 124 of the LSM 108, and another plurality of segments 126forming a lower portion 128 which is mounted upon the floor plates 116,supports a first cylindrical array 130 of storage cells 132 centeredabout the vertical axis A. A second cylindrical array 134 of storagecells 132 is concentrically arranged about the first array 130, mountedupon the wall segments 114 of the outer housing 113.

Because conventional magnetic tape cartridges of the IBM 3480-type aresubjected to an uneven tension upon rewinding of the tape containedtherein, portions of the tape may project away from the wound bodythereby facilitating damage to such portions if stored in a positionwhich would cause undue pressure and potential bending or breakage ofthose portions projecting from the wrapped body. It would, therefore, bedesirable to store such magnetic tape cartridges in a substantiallyupright position to alleviate such problems. The use of the term"upright", it should be apparent, indicates a position in which the axisof the tape reel hub within the cartridge is in a substantiallyhorizontal position, rotated approximately 90° from its transducingposition.

As shown in FIG. 4, when viewed in conjunction with FIG. 3, it can beseen that an access path 136 is formed between the upper and lowerportions 122 and 128 in order that an arm assembly portion 138 ofrobotic means 140 may rotate about the vertical axis A between the firstand second cylindrical arrays 130 and 134. The arm assembly portion 138includes a theta arm 142 rotatably mounted upon a support column 134which is attached to the floor plates 116. The arm assembly portion 138further includes a Z-mechanism 146 attached to the end of the theta arm142 remote from the support column 144. A wrist assembly 148, coupled tothe Z-mechanism 146, is thus provided up-and-down motion as indicated bythe arrows in FIG. 3 for storage and retrieval of magnetic tapecartridges contained within the storage cells 132, and for loading andunloading of the tape cartridges within a selected tape transport 150 ofa tape unit 152 attached to the side of the LSM 108. Each LSM 108, aswill be described in further detail herein below, is capable ofsupporting up to sixteen tape transports 150, four such tape transports150 being arranged vertically on top of one another within a particulartape unit 152. In conjunction with the LMU 106 and a library controlunit (LCU) or inboard controller 154, the robotic means 140 shown inFIGS. 3 and 4 is thus capable of transferring selected ones of theplurality of magnetic tape cartridges contained within the storage cells132 between their substantially upright storage positions and thesubstantially horizontal transducing position at an available tapetransport 150. The LMU 106, as previously described, interprets commandsfrom the host computers 102 and optimizes the motion of the roboticmeans 140 to maximize media handling performance. Each LCU 154, on theother hand, provides the interface between the LMU 106 and the roboticmeans 140, interpreting commands from the LMU 106 and executing motioncontrol sequences of the robotic means 140 within the LSM 108. A remoteelectronics interface (REI) 156, containing amplifiers, power and logiccircuits necessary to drive the robotic means 140 and to utilize avision system 158 (described in further detail herein below), isphysically mounted upon the robotic means 140 within the firstcylindrical array 130.

Referring now to FIG. 5, a presently preferred means for rotating thearm assembly portion 138 of the robotic means 140 is shown. The rotatingmeans preferably comprises a harmonic drive system 160 which includes aservo motor 162 with an integral encoder to monitor the rotation of ashaft 164. An elliptical cam or ball bearing assembly 166 rotates withina flexible, external gear 168, the flexible, external gear 168 rotatingwithin a fixed, rigid internal gear 172. Having two teeth fewer than therigid, internal gear 172, the flexible, external gear 168 providesmotion, through the elliptical cam 166, to the rigid, internal gear 172resulting in a 100:1 reduction ratio of input (shaft 164) to output(theta arm 142). One such harmonic drive suitable for use with theharmonic drive system 160 is manufactured as Model 4M by the EmhartHarmonic Drive Division, Wakefield, Massachusetts. Such a harmonic drivesystem 160 includes a sealed lubrication system, and is easily removedas a single failed replacement unit. Rotational motion provided by theshaft 164 to the can portion 170 is transmitted to the theta arm 142 byconnecting the can portion 170 to an upper plate 174. The upper plate174 may be attached respectively to the theta arm 142 and can portion170 by a machine screw 176 and nut 178 and bolt 180, as illustrated, orsimilar such means. Likewise, the harmonic drive system 160 may suitablybe attached to the support column 144 by a machine screw 182. Smoothrotation of the theta arm 142 about the harmonic drive system 160 maysuitably be ensured by bearings 184.

Also shown in FIG. 5 is a theta arm crash stop mechanism 161 inaccordance with the present invention. Driven by a gear 163 coupled tothe harmonic drive system 160, a smaller gear 165 turns a lead screw 167within the theta arm crash stop mechanism 161. A nut 169 is threadedlycoupled to the lead screw 167, and includes a projection 169a whichtravels up and down within a groove 171 formed in the outer face, of thetheta, arm crash stop mechanism 161. Protection against over rotation ofthe theta arm 142 is suitably provided by the combination of sensors(not shown) for detecting travel of the nut 169, Belleville washers 173which are compressed by the nut 169, or a hard physical stop of theprojection 169 within the limits of the groove 171.

Details of the Z-mechanism 146 and wrist assembly 148 may now beconsidered in conjunction with FIG. 6. As shown therein, a turntablesupport arm 186 supports the wrist assembly 148 for movement in anup-and-down direction (indicated by the arrows in FIG. 4) upon a leadscrew 188 and a pair of guide rods 190. A drive motor 192 drives a shaft194, as monitored by a shaft encoder 196, the shaft 194 coupled to adriver sheave or pulley 198 for driving a belt 200 about a driven sheaveor pulley 202. The driven sheave 202, in turn, is coupled to the leadscrew 188, thereby turning the lead screw 188 within a nut 204threadedly coupled thereto and attached to the turntable support arm186. The turntable support arm 186 is further coupled by linear ballbearings 206 supported upon the guide rods 190. In order to dynamicallybalance the weight of the wrist assembly 148 carried by the turntablesupport arm 186 in the up-and-down motion, a counterweight 208 slidinglysupported upon a pair of guide rods 210 by linear ball bearings 212 isattached to the turntable support arm 186 by a cable 220 lead over apair of pulleys 222. As shown in conjunction with FIG. 7, the drivemotor 192 coupled through the driver sheave 198 and driven sheave 202 iscapable of rotating the belt 200 in either direction (as indicated bythe arrows in FIG. 6) in order to raise or lower the wrist assembly 148mounted upon the turntable support arm 186.

Referring again to FIG. 7, in conjunction with FIG. 6, details of thewrist assembly 148 will now be described. The wrist assembly 148includes a turntable 224 coupled through a driven sheave 226, drive belt228, and driver sheave 230 to a drive motor 232, the rotational positionwhich is monitored by a shaft encoder 234. Situated upon the turntable224, a pair of hand and finger assemblies 236 with their associated rollmechanism 238 are mounted in an opposed relationship not only to provideredundant picking and placing capability for the ACS 100, but also toenhance the speed with which a magnetic tape cartridge is loaded orunloaded in a tape transport 150 without returning to its respectivestorage cell 132. The wrist assembly 148 with its opposed pair of handand finger assemblies 236 is thus designed to reach backward on itselfto take advantage of the storage cells 132 situated upon the inner wall118.

Each hand and finger assembly 236, as shown in FIG. 8, is mounted uponthe turntable 224 at an angle adapted to both adequately and easilystore the magnetic tape cartridges and interface with the loadingposition of the tape transport 150. The angle at which the hand andfinger assemblies 236 may be suitably mounted upon the turntable 224according to the present invention is approximately 10°.

As shown in FIGS. 7-12, each hand and finger assembly 236 is comprisedgenerally of an inner rotatable housing 240 supported by bearings 242within an outer housing 244 attached by means of a foundation plate 246to the turntable 224. A carriage 248 containing a finger mechanism showngenerally at 250 is mounted for extension and retraction upon a leadscrew 252 and guide rods 254. A nut 256, which is threadedly coupled tothe lead screw 252, is also attached to the bottom of the carriage 248.Similarly, a pair of linear ball bearings 258 is attached to the bottomof the carriage 248 for translation upon the guide rods 254. In order tomove the carriage 248 from its fully retracted position as shown in FIG.8 to a fully extended position as shown in FIG. 9, a drive motor 260turns the lead screw 252 thereby extending or retracting the carriage248 upon the nut 256 depending upon the direction of rotation. Onesuitable such drive motor is manufactured as Model 7214B415 by Pittman(a division of Penn Engineering and Manufacturing Corp.) Harleysville,Pa. Attached to the drive motor 260 through a shaft coupler 262 is anoptical encoder 264 for determining the rotational position of the drivemotor 260, and thereby monitoring the translational position of thecarriage 248.

In order to grasp a magnetic tape cartridge, the finger mechanism 250includes a stepper motor 266 attached to the rear of a housing 268containing an over-center toggle 270. One suitable such stepper motor ismanufactured as model number SM-200-0020 by Warner Electric of Marengo,Ill. A lead screw 272 driven by the stepper motor 266 rotates within anut 274 having a yoke portion 276 which is coupled to the over-centertoggle 270 by a pin 278 forming an articulated joint 280. The pin 278 isguided by bushings 279 at either end thereof travelling within a slot281 in the housing 268. As the stepper motor 266 rotates the lead screw272, the nut 274 travels upon the lead screw 272 pushing at thearticulated joint to 280 and causing a pair of opposed fingers 282having gripper surfaces 284 to open away from the magnetic cartridge 286as shown in FIG. 9. Likewise, as shown in FIG. 9, when the nut 274 isrotated upon the lead screw 272 in a direction indicated by the arrowsback towards the stepper motor 266, the over-center toggle 270 returnsto the position shown in FIG. 8, thus closing the gripper portions 284upon the magnetic tape cartridge 286. In accordance with one importantaspect of the invention, and referring now to FIG. 10, a sensingmechanism 288 comprised generally of a plate 290 mounted upon a pair ofrods 292 connected to respective pistons 294 biased in a forwardposition by springs 296 provides feedback on the location of themagnetic tape cartridge 286 with respect to the fingers 282. The sensingmechanism 288 may be suitably attached to the forward part of thehousing 268 by machine screws 298.

Referring now to FIGS. 11 and 12 in conjunction with FIGS. 7 and 8, adescription of the roll mechanism 238 will be given. A roll motor 300mounted upon the side of the outer housing 244 is coupled through adriver sheave 302 and belt 304 to a driven sheave 306 attached to theinner rotatable housing 240. From a substantially horizontal position asshown in FIG. 11, the magnetic tape cartridge 286 is rotatedapproximately 90° by the roll mechanism 238 to the position shown inFIG. 12 corresponding generally to the substantially upright storageposition. Thereafter, the hand and finger assembly 236 may be extendedor retracted as necessary to store the magnetic tape cartridge 286within its respective storage cell 132 or loaded within the tapetransport 150 as will be described herein below with reference to FIG.13-15. The roll motor 300 as shown provides an approximate 5:1 gearreduction, and is controlled by an optical encoder 308. One suitablesuch roll motor 300 is manufactured as model number TOlLB4 by YaskawaElectric of Japan, while a suitable optical encoder is manufactured asmodel number E15 by BEI Motion Systems Company of San Marcos, Calif.

As is also apparent from FIGS. 7, 8, 11 and 12, the vision system 158 iscomprised generally of a charge coupled device (CCD) video camera 310,flanked by a pair of camera lights 312. The camera 310 utilized in apresently preferred embodiment of the invention is manufactured byTakenaka System Co. Ltd. as Pulnix Model TM34K. One suitable such cameralight 312 is a 20 watt, 12 volt model number BAB5582 manufactured bySylvania. As is conventional, the field of vision of the camera 310 isdivided up into a number of pixels. Through illumination of a uniquetarget by the lights 312, the target being advantageously locatedproximate to a storage cell 132, the camera 312 can project an imagewhich is compared to an image corresponding to an ideal position forstoring or retrieving the magnetic tape cartridge 286, therebyfacilitating fine positioning through feedback. The camera 312 may alsobe conventionally employed to read a VOLSER (i.e., volume serial) labelconsisting generally of OCR characters and bar codes.

Referring now to FIGS. 13-15, there is shown a carriage assembly of thetape transport 150 according to the present invention. The tapetransport itself may be suitably comprised of a conventionalself-threading, reel-to-reel drive compatible with IBM 3480-typemagnetic tape cartridges, as described in U.S. Pat. Nos. 4,334,656 and4,399,936, and in Winarski et al, "Mechanical Design of the Cartridgeand Transport for the IBM 3480 Magnetic Tape Subsystem", IBM J. Res.Develop., Vol. 30, No. 6 (November 1986), pp. 635-44, each of which isincorporated herein by reference. However, the carriage assembly 314according to the present invention interfaces with the drive (FIG. 16)in order to expedite loading and unloading of the magnetic tapecartridge 286. The carriage assembly 314 includes a tray 316 which isadapted to move the magnetic tape cartridge 286 from its unloadedposition as shown in FIG. 13 to a loaded position as shown in FIG. 14.The tray 316 includes the top plate 318 and bottom plate 320 withrespective notches 322 and 324 adapted to permit the fingers 282 of therobotic means 140 to insert the magnetic tape cartridge 286 within thecarriage assembly 314 for loading and unloading thereof.

When a particular magnetic tape cartridge 286 is desired to be loadedupon the tape transport 150 for reading or writing of data, the roboticmeans 140 inserts the magnetic tape cartridge 286 within the tray 316. Acartridge present switch 326 is activated by its flag 328 throughphysical contact with the magnetic tape cartridge 286. Meanwhile, asmall roller 327 biased by a spring 328 attached to the bottom plate 320is utilized to retain the magnetic cartridge 286 within the tray 316.The tape transport 150 is interrogated via a tape unit interface asdescribed in detail below to determine if the magnetic tape cartridge286 has been fully entered into the tray 316. A second switch 330 andits associated flag 332 are also included within the carriage assembly314 to detect the conventional file protect mechanism of the magnetictape cartridge 286. Upon activation of the cartridge present switch 326,and a subsequent command from the LCU 109, a drive motor 334 isactivated in order to rotate a first gear 336 which in turn drives asecond gear 338. Coupled through a shaft 340, the second gear 338transmits its drive force to a pair of cams 342 located on either sideof the tray 316. Pins 344 contained with the cams 342 and attached torespective pivot arms 346 force the carriage assembly 314 up or down ascontrolled by the drive motor 334. At the same time, the top plate 318is biased down against the magnetic tape cartridge 286 by four springs348 attached to the corners of the top plate 318, thereby transmitting auniform pressure to the magnetic tape cartridge 286, holding it in placefor engagement with a drive hub 350. When the reading or writing of datafrom the magnetic tape cartridge 286 is completed, the carriage assembly314 is rotated up from its loaded position shown in FIG. 15 to itsunloaded position shown in FIG. 14 by the drive motor 334, whereupon themagnetic tape cartridge 286 may be urged outwardly from he tray 316 byany suitable ejection means.

As shown in FIG. 16, each tape transport 150 is controlled by a tapecontrol unit 111. The carriage assembly shown in FIGS. 13-15 isoperatively coupled to the tape drive 315. Threading is accomplished bya pantocam threader that guides the leader block of the magnetic tapecartridge 286, to which the tape is attached, around the tape path. Theleader block is inserted into the take-up reel, and the tape is broughtto the correct tension to complete the threading operation. Guiding ofthe tape over the magnetic head is accomplished by compliant guidesseating the tape against referenced flanges. Further details of theoperation and mechanical components of a suitable tape drive portion 315may be found in through reference to Winarski et al.

The tape control unit (TCU) 111 manages the writing and reading of datato and from attached tape transports 150. It receives commands from oneto four channels, decodes these commands, selects transports and issuescommands to them, passes data from channels to transports, returns datafrom transports to channels, and sends transport status to channels.FIG. 16 includes a block diagram of the TCU 111.

There is one channel adapter 317 for each channel connected to the TCU111. It receives control signals and data from the channel interface andpasses data to a data buffer 319, from which it goes to the tapetransport 150. It receives data and status from the data buffer 319,passing it to the channel interface.

Data transfer control logic 321 handles the flow, commands, and statusbetween the channel adapter 317 and data buffer 319, and checks data foraccuracy. When data passes to the data buffer 319, this checking logicgenerates two check bytes and apends them to the data. When the data isread from a tape transport 150, as it passes through this logic back tothe channel, the logic generates two check bytes and compares them tothe check bytes generated when the data was written on the tape. If thecomparison is not perfect, an error has occurred somewhere and the datacannot be trusted.

The channel adapter 317 is an "intelligent" channel adapter. As such, ina dual-TCU 111 configuration it queries a status store, it determines towhich data buffer 319 a job is assigned, and interrupts the appropriateprocessor instead of always interrupting its own, thereby increasingefficiency. It also means that load balancing is done to increasethroughput, not to remove data bottlenecks in the controller. That is,the channel adapter does the load balancing automatically without havingto disturb the processor, which might decide to balance the load becausedoing so would take longer than processing the data itself.

The data or cache buffer 319 is a first-in, first-out dynamic RAMbetween the channel adaptor 317 and tape transport 150. It masks theinherent slowness of a mechanical transport system and permits datatransfers to and from the cartridge subsystem at channel speeds. Whiledata to and from the transport 150 flows at a rate proportional to thespeed of the moving tape, the channel can begin writing to the databuffer 319 while the tape is coming up to speed. It can write in thedata buffer 319 the data it wants to transfer, and disconnect, leavingthe data buffer 319 to send the data to the transport 150 withoutfurther involvement of the channel. In a read operation, the channelwaits until all or most of the data from the record on the tape is inthe data buffer 319, then reconnects to the channel and transfers thedata. During read operations, if an attempt to correct data withoutstopping the transport 150 fails, data is taken from the data buffer319, looped back to the repath, and correction is attempted usingvarious algorithms beyond current 18-track hardware correctiontechniques.

The channel side control processor 323, also known as channel processor,is a complete microprocessor that controls all activity on the channelside of the TCU 111. In a presently preferred embodiment of theinvention, it consists of a high power, 16-bit microprocessor chip, withassociated EPROM and RAM memories, clocks, interrupt handlers,registers, and parity generators and checkers. As such, the channelprocessor 323 is a multi-tasking, interrupt-driven processor. Itresponds immediately to tasks with a high priority than the task it isprocessing and stores a program address in memory, so that it can returnto the previous job where it left off.

A device side control processor 325, structurally identical to thechannel processor 323, controls data flow between the data buffer 319and tape transports 150. Separate processors for channel and deviceactivity thus means that both sections receive top priority, because oneprocessor does not have to divide its time between the two tasks, thetwo tasks being serviced simultaneously. In addition, both processors323 and 325 are interrupt-driven and have multi-task operating systemswhich enable a fast and efficient cartridge-type control unit.

The status store 327 is a logic collection that speeds up the TCU 111handling of data. It connects the channel adapters 317 and channelprocessor 323 in a TCU 111 and stores channel adapter, control bytes,and status bytes. Communication between the channel adaptor 317 andchannel processor 323 are stored in status store 327. Each unit reads orwrites to status store 327 to communicate with the other unit. A channeladapter 317 and the channel processor 323 need not wait until both arefree to communicate. If a channel adapter 317 is busy, the channelprocessor 323 writes a message in status store 327 and is free to dosomething else, thereby increasing throughput. When the channel adapter317 is free, it reads the message. A channel adapter 317 communicateswith the device processor 325 in the same way.

In dual-TCU 111 configurations, the channel adapter 317 and channelprocessor 323 in a TCU 111 communicate with the channel adaptor 317 andchannel processor 323 in the TCU through their status stores 327. Thetwo status stores 327 are connected through a remote control interface,and whenever a channel adapter 317 or channel processor 323 writes toits status store 327, the same information is written to the statusstore 327 in the other TCU 111. A channel processor 323, therefore, isaware of the state of the channel adapter 317 in the other TCU 111. Itcan determine to which data buffer 319 a job is allotted without havingto query the processor 323 in the other TCU 111.

As described herein above, the device side control processor 325, alsoknown as device processor, controls everything on the transport side ofthe data buffer 319. This includes establishing data path connectionsbetween devices and the assigned data buffer 319, either local orremote, initiating transport motion and read or write data transfersbetween the data buffer 319 and the transports 150 through the deviceinterface, and controlling non-data blocks, such as tape marks.

A read sequencer 329 converts tape data pulses that it receives in ANSIformat from the transport preamplifier through the device interface,into digital channel data, and sends it to the data buffer 319. At thesame time, it checks the data for errors and corrects any error, ifpossible. The device processor 325 controls the read sequencer 329 whichis active also during write operations. That is, it checks write databefore that data is sent to the transport 150.

A write sequencer 331 receives channel data from the data buffer 319,converts it from digital channel format to ANSI type format, and sendsit to the transport 150 through the device interface. It alsoregenerates check characters and compares them to the charactersgenerated and appended to the data when it goes through data transfercontrol 321. The write sequencer 331 also generates the data patternsfor inter-block gaps, tape mark, density identifier, and erase gap. Thedevice processor 325 also controls the write sequencer 331.

A device adaptor 333 manages traffic through the device interface to andfrom attached transports. There are two device interfaces: local, totransports attached directly to the TCU 111; and remote, to another TCU111 and its transports.

The device adaptor 333 converts commands from the device processor 325and data from the write sequencer 331 into protocol proper to a3480-type device interface.

Communication memory 335 is a two-port, 16 K-byte static RAM memorylocated logically between the channel processor 323 and the deviceprocessor 325. The two processors have equal access to this memory andcommunicate with each other through it. Each processor can address thismemory to find out the status of data transfers, and the memory caninterrupt either processor. The two processors work independently andare not held up by a need to communicate directly with each other. Assuch, the TCU 111 has substantially increased throughput.

A maintenance facility 337 consists generally of hardware and softwarethat let both an operator and a remote diagnostic facility monitorsubsystem conditions and diagnose problems. Components of themaintenance facility 337 include a control panel, local and remote RS232 diagnostic ports, a comprehensive diagnostic package, and an expertsystem.

Referring now to FIGS. 17-19, the means for manually inputting andoutputting a plurality of the magnetic tape cartridges 286 will beexplained. As shown in FIG. 17, one wall segment 114 of the outerhousing 113 of the LSM 108 includes a hinge 356 in order to open thatpanel and permit access to the interior of the LSM 108. Likewise, theinner wall 118 includes a hinged portion 358 at the lower 128 for accessto the robotic mean 140 contained therein. A support wheel (not shown)may be utilized to prevent the weight of a plurality of cartridgesstored in the hinged portion from distorting the hinge.

The wall segment 114 comprising the access door 360, as shown in FIG.18, also includes a cartridge access port 362 for manually inputting andoutputting a plurality of cartridges 286 as will be described in greaterdetail herein below. The cartridge access port or CAP 362 includes afixed array of storage cells 132 similar to those mounted upon the innerwall 118 and wall segments 114. The CAP 362, as shown more clearly inFIGS. 19 and 20, includes a door 364 having a hinged portion 366 whichpermits the door to swing outward from the outer housing 112, therebyexposing the array of cells 132 for manual input or output by anoperator. A gas spring 368 aids opening and prevents the CAP 362 fromslamming shut, dislodging cartridges 286 contained therein, and providesa means for smoother operation of the CAP 362 through use of a dampeningdevice internal to the gas spring 368. In accordance with one importantaspect of the invention, a means is provided to ensure the safety of anoperator and still permit continuous operation of the robotic means 140.That means, as shown in FIGS. 19 and 20, comprises an articulated wallportion 370 which closes the opening in the outer housing 112 upon theopening of the CAP 362. The wall portion 370 may suitably be comprisedof a plurality of lightweight, flexible segments 372 hinged together atpivot points A, and B. The segment 372 at point C is attached to a pairof cam followers 374 which ride in a cam groove 376 formed in the upperand lower portions 378 and 380 of a cap housing 382. Therefore, when theoperator opens the door of the CAP 362, the articulated wall portion 370is drawn across the opening left by the door 364, thereby preventingaccess to the operating robotic means 140.

In accordance with yet another important aspect of the invention, thereis shown in FIG. 21a one means for transferring a plurality of thecartridges 286 between LSMs 108 which are attached to one another.Referring also to FIG. 2, 22 and 23, it is apparent that futureexpansion of the library means is possible through interconnection ofmore than one LSM 108 in groups of two, three or four or more due totheir twelve-sided configuration. Where the LSMs 108 are connected oneto the other, a pass through port 382 according to the present inventionis provided to transfer a plurality of the magnetic cartridges betweenthe interconnected LSMs 104. As shown in greater detail in FIG. 21a, thepass through port 382 is comprised generally of multiple storage cells132 adapted to ride upon a carriage 384 for transference between theLSMs 108. The array of storage cells 132 are spring-loaded upon a pivot386 attached to the carriage 384, and includes a pair of cam followers388 adapted to follow a cam surface 390 from one LSM 104 to the other.The carriage 384 is further coupled to a lead screw 392 by a nut 394(not shown for clarity) which conventionally pulls the carriage 384along the lead screw 392. In order to guide the carriage 384 along thelead screw 392, the carriage 384 is further coupled to a pair of guiderods 396. When a drive motor 398 rotates the lead screw 392, thecarriage 384 is pulled along the lead screw 392 by the nut 394, but thepivoting array of cells 132 following the cam surface 390 enable thecells 132 to be positioned advantageously for incorporation with eitherLSM 104. That is, the array of cells 132 are initially positioned withinone LSM 108 in a manner similar to each of the other storage cells 132mounted upon the outer housing 112 of the LSM 108 for access by therobotic means 140. Thereafter, upon rotation of the lead screw 392 bythe motor 398, the array of cells 132 are rotated (as shown by thedashed arrows in FIG. 21) to a position within the interconnected LSM108 for access by its respective robotic means 140, the phantom linesillustrating the array's rotated position. It should be noted at thisjuncture, however, that the carriage 384 does not enter the arm swingspace so that motions of the robotics 140 may continue during rotation.

An alternative, and presently preferred embodiment of a pass throughport 382a is shown in FIGS. 21b and 21c. Like the pass through port 382shown in FIG. 21a, the pass through port 382a includes a pair of camsurfaces 390a and 390b, each of which are referenced to their respectiveLSM 108. A lead screw 392a and nut 394a arrangement provides the motiveforce for translating the carriage 384a between the LSMs 108, and atorsion spring 384 is used to pivot the cells 132 just as in the passthrough port 382 of FIG. 21a. However, instead of guide rods 396, thecarriage 384a is by a simple groove 395 and pin 397 arrangement whichmaintains its stability.

Referring now to FIG. 22, there is shown a typical array of storagecells 132 which may be utilized in accordance with the presentinvention. While the array shown in FIG. 22 has a radius of curvatureadapted to be mounted upon the inner wall 118 of an LSM 104, it shouldbe understood that individual cells 132 may be formed with an oppositecurvature in order to be mounted upon the wall segments 114 of the outerhousing 112. The cells 132 may also be formed in linear arrays forincorporation within the pass through port 382 or the cartridge accessport 362. In any case, the cells 132 as shown in FIG. 22 are comprisedgenerally of a bottom portion 402, back portion 404, and interveningwall portions 406 to provide a plurality of slots or cells 132 forstorage of the cartridges 286. The wall portions 406 are adapted foraccess by the hand and finger assemblies 236 of the robotic means 140.Suitable means, such as the hooks 408 formed at the rear of the array ofcells 132 may be used to suspend the cells 132 from the wall segments114, 120, 126, or within the cartridge access port 362.

As stated herein above, the LMU 106 is the controlling function of theACS 100. It acts as the interface between the host computers 102 and theLSMs 108. The major components of the LMU 106, and their functions, aredescribed herein below.

Referring now to FIG. 23, which shows a block diagram of the LMU 106according to the present invention, it can be seen that the LMU 106 iscomprised generally of a central processor module (CPM) 500, sixteeninterface processor modules (IPM) 502, a LMU bus 504, a LMU operator'spanel 508, a pair of floppy disks 510, a power monitor 512, andmaintenance port 514. The CPM 500 provides the hardware necessary tohandle all library management functions, and to support maintenance anddiagnostic needs, and is attached to a memory (MEM) card 520 containing512 kilobytes of static random access memory and 4 kilobytesprogrammable read only memory, and a peripheral interface module (PIM)card 522 which provides the logic necessary for communication with aplurality of LMU interfaces 524 (FIG. 24). Such interfaces may include aLMU bus interface 524a, a maintenance computer A interface 524c, amaintenance computer B interface 524d, a floppy disk interface 524e, aLMU operator's panel interface 524f, a local area network (LAN)interface 524g, and a power monitor interface 524h. Communication witheach of the interfaces 524 is accomplished by accessing externalregisters which will be described in further detail herein below.

In order to control each of the elements of the LMU 106, the CPM 500utilizes an internal microprocessor 518, which may comprise aconventional Z8002 microprocessor, to implement the interface betweensoftware and hardware in the CPM 500. To provide this control, theregisters in each of the CPM interfaces 524 are mapped into the memoryspace of the microprocessor 518. The microprocessor 518 communicateswith the interfaces 524 by reading and writing such external registersto initialize the individual interface. Controller chips may be used toimplement the individual interfaces in order to off load control of theinterface attachment as much as possible. Such interface controllersimplement the protocol, control, and data handling with the attacheddevice. As such, the microprocessor 518 is only involved in initializingthe controllers, passing data between the interfaces, and errorhandling.

As is well known, the Z8002 microprocessor 518 is a conventional 16-bitmicroprocessor with a 16-bit bus that can operate at an eight megahertzclock rate. Program memory on board the CPM 500 is provided by 4kilobytes of program programmable read only memory (PROM) and 256kilobytes of partially paged program static random access memory (RAM).An additional 256 kilobytes of data memory are also provided. The datapassed between the various components of the CPM 500 are illustrated inFIG. 24.

Referring again to FIG. 23, when viewed in conjunction with FIG. 24, itis apparent that the CPM bus 526 is internal to the CPM 500 and consistsof those signals necessary to transmit data between the microprocessor518 and other logic on the CPM 500. Each of the interfaces 524 on theCPM 500, as shown in FIG. 24 is provided for CPM input/outputinterfacing. For example, the LMU bus interface 524a provides the CPM500 with the capability of communicating with an IPM 502 over the LMUbus 504. The maintenance computer interfaces 524c and 524d provide theCPM with the capability of interfacing to a maintenance computer (notshown) and modem or modem junction box for remote maintenance. Thefloppy disk interface 524e provides the CPM 500 with the capability ofattaching conventional 51/4 inch mini-floppy disks. The LMU operator'spanel interface 524f provides the CPM with the capability of interfacingto switches and indicators external to the CPM 500. Two identical, LANinterfaces 524g provide attachment to the LSMs, one being provided asprimary and the other as backup. A physical BNC connector is alsoprovided for connection of a maintenance device to each of the LANs,while four programmable timers are provided on the CPM 500 acting asgeneral purpose timers. The CPM 500 may also contain a real time clockpowered by a long-life battery to maintain system time during power off.

As shown in FIGS. 25a and 25b, the CPM 500 consists generally of a PROMprogram memory, and data memory which serves as private memory for themicroprocessor 518. The program PROM is read only memory that retainsits contents when powered off, and may be suitably implemented usingconventional 2K×8 PROMs to provide a word-wide memory. Parity is notused and PROM content can be verified by software. The PROM occupiesboth system and normal program space to allow for initial program loadand other common routines.

FIGS. 25a and 25b, illustrative of memory paging, is broken up intothree sections. The first on the far right shows the physical memory asit exists in hardware. Side-by-side 32K×8 SRAMs denote the mostsignificant byte on the left and the least significant byte on theright, constituting a block of memory 64 k bytes long. Note that arefour blocks of data (A-D) and four blocks of program memory (E-F) for atotal of 512 k bytes of memory.

Block D (data) contains the common data space. It also contains the SRAMthat is "covered up" by input output devices (255 bytes). This commondata space is the physical memory that will be accessed if the virtualaddress from the microprocessor 518 is not in the paged area of memory.Likewise, in block H of program space, the common program space residesalong with the SRAM that is "covered up" by the PROM- (four kilobytes).

The middle column of FIGS. 25a and 25b denotes the LANCE linearaddressing of memory from address HEX 00000 to 7FFFF. Note that softwaremust perform an address translation if it attempts to address memory toaddress memory that the microprocessor 518 has been addressing as pagenumber n page size s.

The columns on the left side of FIGS. 25a and 25b show memory broken upinto its different page sizes and numbers. Each column denotes adifferent page size, each space (program and data) being capable ofhaving different page sizes and numbers. Within each column the pagenumbers that reside in that physical block of memory are given. Forinstance, if the data page size is 16 k, block A will contain four 16pages 00,01,02, and 03 (page numbers are given in HEX . Block B willcontain pages 4-7, and so on. Therefore, if the data page size is 16 kand the page number is 02, the block of memory addressed will be blockA. Paging is envoked only if the virtual address is in the paged area.In the data space, the paged area resides at the low addresses ofmemory, while in program space the paged area is at the high addressesof memory (FFFF is "higher" than 0000). As a result, in the data spaceif the size is 16 k virtual addresses 0000 through 3FF HEX are the pagedarea of memory. For a page size of 4 k, 0000 through 0FFF is the pagedarea of memory. The other virtual addresses (4000 and above four 16 ksize) therefore, suppose the microprocessor 518 has written to the datapage register with a 10000011 which selects a page size of bits 7, 6=1,0=page size of 16 k and a page number of 000011=page number 3 HEX. Ifthe microprocessor 518 places a virtual address on the bus that is inthe paged area (less than 4000 for this size) then the paging will occurand the virtual address will be translated in hardware so that block Ais selected and page is addressed. If, however, the microprocessor 518had put out an address that was not in the paged area (i.e., greaterthan or equal to 4000 for page size 16 k) then the paging would notoccur and the common data space would be selected which is in block D. Asimilar case holds for the program space except that the paged area isat the high end of memory as mentioned above.

When paging is envoked by the microprocessor 518 accessing a virtualaddress in the paged area, the physical address to the memory isdetermined as follows. The block is selected as mentioned above based onthe page size and number. Then, the physical address presented to thatblock is arrived at by translating the upper virtual address bits toaccess the desired location in that block. For instance, if data pagesizes 16 k, page number 02 HEX, and the virtual address is 2000 HEX,then block A will be selected. The virtual address bits will betranslated by adding the offset into the paged area, in this case 2000HEX, to the starting address of the desired page, in this case 8000 HEXor page number 02, for a final physical address of 8000+2000=A000 HEX toblock A.

A similar situation exists for the program space except that since thepaged area is at the high end of block H, the offset into the paged areamentioned above is determined by subtracting from the virtual addressthe starting of the paged area. For example, for program page size 8 k,program page number 11, virtual address E 100 the following will occur.Block G will be selected and the physical address will be the offsetinto the paged area. For program AK pages E000 is the stating address ofthe paged area as shown in the table above.

System and normal memory may be suitably implemented using 32K×8 staticRAMs to provide a word-wide (2 byte) memory. Odd parity is used on eachbyte of the RAM. The program PROM displaces the first 4096 words ofsystem and normal program memory and leaves such memory unaccessible.External registers, as shown in FIGS. 26a and 26b, displace the upper256 bytes of system and normal data memory and leaves such memoryunaccessible.

All CPM external registers are addressed as memory addresses. Parity isnot checked when reading external registers.

As shown in FIGS. 26a and 26b, B indicates a register size which isaddressable as a byte or word but will only provide useful data on theleast significant byte. The most significant byte will be FF. A registerwhich can be accessed as a word or as independent bytes is indicated byB/W., It should be noted that all reads are word reads but that themicroprocessor 518 only pays attention to the byte selected if in bytemode. Also, on byte mode write the microprocessor 518 duplicates theselected byte on both the most significant byte and least significantbyte of the bus. A LW indicates a long word address which should only beaccessed as a long word (i.e., 32 bits).

The type of registers are also indicated in FIGS. 26a and 26b by theabbreviation NO, RO, and R/W. A no type indicates that the address isnot valid. No error will result is accessed but useful data cannot bewritten or read. RO indicates read only, but writing to this addresswill cause no effect. On the other hand useful information is availableby reading this address. Finally, R/W indicates a register which can bewritten or read. Descriptions of the individual registers may be foundin Appendix A. One provides all the control functions involved incommunicating with the IPMs 502 over the LMU 504. LMU bus status isindicated in the register at address FF02 thereby providing statusinformation on the success or failure of an LMU bus transaction. Itshould be noted that the NACK and module busy are valid only after a CPMtransmission when the output device (FIFO or info out register) showempty and plus status cycle transmit is inactive.

The LMU bus 504 is fully synchronous with a cycle time of 250nanoseconds, and provides a bandwidth of four megabytes per second. Itallows various modules to connect to the bus and communicate with eachother. Information is transferred on the LMU bus 504 during atransaction between two modules, one acting as the bus master and theother as the bus slave. A transaction is composed of multiple bus cyclesof various types and transactions can be overlapped or pipelined suchthat a new transaction can be initiated while a previous transaction iscompleting. When a module wishes to use the bus 504, the particularmodule requests bus access and then determines whether the bus isgranted by monitoring bus signals. When the bus is granted, the modulebecomes the bus master. The bus master will then initiate a bustransaction with the bus slave, priority being established forarbitration by the physical positioning of the modules in the backplane. When bus usage is granted, the bus master transfers informationto the bus slave module in one or more transfer cycles immediatelyfollowing the arbitration cycle. These transfer cycles are referred toas outbound transfer cycles. For each outbound transfer cycle, the slavemodule responds with status in the following cycle. Any externalconditions causing termination of a module operation must allow themodule to finish the bus transaction, if possible, before termination sothat the bus remains in operation and other modules are not affected. Ifthis is not possible, Bus Busy is negated to free the bus forarbitration and further use. As shown in FIG. 40, the arbitration cycleends status cycle can occur concurrently for two separate transactions.

The LMU bus 504 uses a time slot, multiplexed, design which allows a newtransfer to be placed on it every bus cycle (except when arbitration istaking place). Arbitration is by a distributed means with fixed priorityaccording to the physical positioning of modules in the back plane.

Operations of the LMU bus 504 are divided into three types: CPMRequests, IPM Requests, and Information Transfers as described hereinbelow. CPM Requests cause one byte of information to be sent from theCPM 500 to the addressed IPM 502.

The info out register is first loaded with the byte plus parity to betransmitted to the IPM 502. Thereafter, the address out register isloaded with the four-bit address plus parity of the IPM 502 to which theinformation is to be sent. The LMU control register is then addressedand loaded with "100000101" which causes or keeps the status reset flipflop enabled, asserts the CPM Request signal, and asserts the LMU BusEnable Signal. At this point, the microprocessor 518 may perform othertasks since the rest of the CPM Request process is hardware implemented.However, the microprocessor 518 must perform a status check after theCPM Request to verify a successful operation.

LMU Bus Request asserts causing LMU bus arbitration. The CPM 500 willwin the bus arbitration unless a FIFO transfer is in progress. If suchFIFO transfer is in progress, the CPM Request logic will continue toarbitrate until the bus is granted at the completion of the FIFO oruntil the microprocessor 518 negates the CPM Request signal. It shouldbe noted at this juncture that the LMU Bus Request signal (arbitration)must be asserted for at least one clock cycle to prevent one or theother IPMs 502 from successfully being rented the use of the LMU 504. ALMU Bus Grant asserts on the rising edge of the clock followingsuccessful bus arbitration. Data in the form of address out and info outis then placed on the LMU bus 504 on the rising edge of the next clock.

All of the IPMs 502 compare the module address, on the LMU bus 504,against their individual physical addresses. The one IPM 502 that has asuccessful compare enables its logic to receive the data from the LMUbus 504.

The IPM info in register is then loaded with the data on the LMU businformation lines, and the IPM 502 checks the parity of the informationand address data from the LMU bus 504. If good parity is detected, theIPM 502 will assert-acknowledge on the next rising clock edge,indicating a successful reception of data. If bad parity is detected, -Acknowledge will not be asserted.

Thereafter, the CPM 500 checks the status of the - Acknowledge signal.If negated (high) the CPM 500 will initiate a - Not AcknowledgeInterrupt. This means that either none of he IPMs 502 saw the correctmodule address, or an IPM 502 did get a successful address compare butdetected a parity error in the information or module address. If -Acknowledge is asserted, one of the IPMs 502 successfully compared themodule address to its own and detected good parity on the informationand module address. This indicates that the CPM 500 sent the data outcorrectly and one of the IPMs 502 recognized it. By reading the CPMstatus register the microprocessor 518 checks the status of the - ModuleBusy Signal. If asserted, the IPM 502 recognized the CPM Request but wasunable to load the information into the CPM Info In Register because theregister had not been read since the previous transmission from the CPM500. At this point, the microprocessor 518 may attempt a retry orretries. If negated, the CPM Request was successful in transmittingrecognizable from the CPM 500 to the IPM 502 and the transfer wasaccepted by th IPM 502. Finally, the - Status flip flop reset in the LMUcontrol register is asserted (low) to reset the CPM Request logic forfurther activity.

IPM Requests cause one byte of information to be sent from a IPM 502 tothe CPM 500. The CPM 500 then reports status back to specify the successor failure of the IPM Request, which may be implemented as follows. TheIPM info out register is first loaded with the byte, plus parity, to betransmitted to the CPM 500. Thereafter, the IPM address out register isloaded with the IPM's 4-bit physical address, plus parity, to identifyto the CPM 502 sent the data. The IPM 502 then loads its left bandaddress register with "XXX10000" which enables the Write IPM controlregister signal on the next master clock rising edge. Hardware logic isthen initiated by the IPM control register being written with "01000000"which asserts the IPM Request signal. Bus arbitration, by the IPM 502,begins with the assertion of the physical address request enable signalfor a minimum of one 4 megahertz clock signal, which if arbitration issuccessful, will result in Bus Grant being asserted to enable the outputof data from the IPM 502. If arbitration is not immediately successful,the PAR REQ EN signal will remain asserted until the bus is read or theIPM MPU stops the IPM Request operation.

The address out and info out registers are next output onto the LMU bus504 as the - IPM Request signal output to the bus is negated. Then, theCPM 500 loads the data from the LMU bus 504 into its info in and addressin registers. The CPM 500 sets the status bits - ACK n-Module Busy. ACKis asserted if the CPM 500 detected good parity in the data transmittedto it from the IPM 502. - Module Busy is asserted if the CPM info in andaddress in registers have not been read/cleared since the last IPMRequest. The IPM 502 subsequently checks the - Acknowledge signal, andif negated (high) a Not Acknowledge interrupt is generated in the IPMMPU indicating that the CPM 500 was unable to receive the data becauseit didn't see the IPM Request signal or that the data that was receivedhad bad parity. Module Busy In may then be loaded by the IPM 502 intothe IPM status register. If asserted, this indicates that the CPM 500successfully received the data but was unable to load its info andaddress in registers with the data. If negated, the CPM 500 successfullyreceived and loaded the data transmitted during the IPM request. Afterthe IPM Request is completed, the CPM 500 asserts its Input Buffer FullSignal indicating that info and address and registers have data in themthat has not been read. This signal must be negated by the CPM 500 afterit reads its info in and address in registers. Finally, the CPM 502resets the Bus Status flip flops to prepare for further activity.

Information Transfers are used to transfer a block of data between twoLMU bus modules. The information is transferred from the output FIFObuffer of the master module to the input FIFO buffer of the slavemodule. Two types of FIFO transfers are possible. A IPM FIFO transfer,which transfers a block of data from the IPM 502 to the CPM 500, and aCPM FIFO transfer, which transfers a block of data from the CPM 500 toan IPM 502.

In a IPM FIFO transfer, the IPM 502 loads its output FIFO with up to 512bytes of information. The IPM 502 then notifies the CPM 500 of theimpending FIFO transfer using the IPM Request discussed herein above.The CPM 500 prepares for the transfer and notifies the IPM 502 when itis ready to receive the data. By software command, the IPM MPU addresses"XXX10000" to select the IPM control register. Afterwards, the IPMcontrol register is loaded with "10000000" to command the IPM hardwareto perform the IPM FIFO transfer (i.e., data transfer asserts). At thispoint, the IPM MPU may perform other tasks as further intervention inthe transfer process is not required. The data transfer signal assertsthe physical address of the IPM 502 onto the parallel request lines (LMUbus arbitration). This will continue for a minimum of one cycle throughbus grant to the completion of the transfer operation. As a result, theIPM 502 is granted the bus when the bus arbitration is successful (busgrant asserts).

On the next rising 4 megahertz clock, the IPM 502 asserts - IPM DAV onthe LMU bus 504, thus notifying the CPM 500 that the transfer of bytedata will begin in this cycle and continue until - IPM DAV negates(i.e., the transfer operation is complete). The IPM 502 then asserts itsmodule onto the LMU bus 504, remaining in effect until the end of thetransfer operation. Thereafter, the read strobe to the IPM output FIFOis enabled causing data to be read from the FIFO to the LMU bus 504 1byte per clock cycle until the transfer operation is complete. The CPMinput FIFO Write strobe (IF WR) strobes the data onto the CPM input FIFOfrom the LMU bus 504, 1 byte per clock cycle until the IPM 502 signalsthat the transfer operation is complete (-IPM DAV negates).

On the next clock cycle, following each byte transfer, the CPM 500asserts the -Acknowledge signal if good parity was detected in thetransfer byte and the IPM module address is transferred in the previouscycle. The IPM 502 will interrupt if -ACK is not asserted. The IFOtransfer will continue to completion regardless of a parity error. Whenthe IPM output FIFO empties (transfer operation complete) - IPM DAV willnegate on the next rising clock causing the data transmission to stop.The IPM module address is removed from the LMU bus 504, bus arbitrationis allowed for other modules, the CPM 500 stops writing data into itsinput FIFO, and the CPM 500 disables its status outputs (-ACK) on thenext rising clock. This completes the IPM FIFO transfer operation, andthe LMU bus 504 is free for other traffic. The microprocessor 518 seesthat the CPM input FIFO is not empty, and will initiate DMA transferfrom the input FIFO to the CPM memory.

For a CPM FIFO transfer, the CPM 500 first loads its output FIFO with upto 512 bytes of information using the microprocessor 518. Thereafter,the CPM 500 notifies the IPM 502 of the impending FIFO transfer usingthe CPM Request, discussed herein above. The IPM 502 prepares for thetransfer and notifies the CPM 500 when it is ready to receive the data.Then the microprocessor 518, by software command, addresses flip flop"0001110X" to select the LMU control register.

As the LMU control register is loaded with "10000111" to command the CPMhardware to perform CPM FIFO transfer (FIFO REQ asserted), themicroprocessor 518 may perform other tasks as further intervention inthe transfer process is not required. The FIFO REQ signal then assertsthe physical address of the CPM 500 onto the parallel request lines (LMUbus arbitration), and continues so for a minimum of one cycle throughbus grant to the completion of the transfer operation. The CPM 500 isgranted the bus when the bus arbitration is successful (bus grant), andon the next rising four megahertz clock, the CPM 500 asserts -CPM VAV onthe LMU bus 504 thus notifying the IPM 502 that the transfer of bytedata will begin in this cycle and continue until -CPM DAV negates (i.e.,the transfer operation is complete).

The CPM 500 asserts the module address of the IPM 502 onto the LMU bus504, and remains so in affect until the end of the transfer operation.One byte of data per clock cycle is then read from the FIFO to the LMUbus 504 after the read strobe to the CPM output FIFO (-OF RD) isenabled. Such reading also continues until the transfer operation iscomplete. The IPM 502 that successfully compares the module address fromthe LMU bus 504 to its own physical address will, using the IPM inputFIFO Write signal (WR FIFO IN), strobe the data into the IPM input FIFOfrom the LMU bus 504 one byte per clock cycle until the CPM 500 signalsthat the transfer operation is complete (-CPM DAV negates).

On the next clock cycle following each byte transfer, the IPM 502asserts the -Acknowledge signal if good parity was detected in thetransfer byte and the IPM module address was transferred in the previouscycle. If none of the IPMs 502 successfully compare the module addressto their own physical address -ACK will not be asserted. The CPM 500will interrupt if -ACK is not asserted, and the FIFO transfer willcontinue to completion regardless of the -ACK interrupt. When the CPMoutput FIFO empties (transfer operation complete) -CPM DAV will negateon the next rising clock. This causes the data transmission to stop, theIPM module address is removed from the LMU bus, bus arbitration isallowed for other modules, the IPM 502 stops writing data into its inputFIFO, and the IPM 502 disables its status output (-ACK) on the nextrising clock. This completes the CPM FIFO transfer operation, and theLMU bus 504 is free for other traffic. The IPM MPU sees that the IPMinput FIFO is not empty and will initiate a transfer of the data fromthe input FIFO to the IPM memory.

All signals on the LMU bus are conventional TTL signals. When the bus isin a quiescent state, termination pulls all signals high. Arbitrationcycle signals are comprised generally of a parallel request and a busbusy. The parallel request includes four open collector signals whichcarry the binary waited request to all modules on the LMU bus 504. Amodule desiring bus master status, asserts its physical address onto theparallel request lines during the arbitration cycle. The wire AND resultof these lines is then compared to the physical address of the moduleand, if the comparison proves valid, that module becomes the bus master.The bus busy arbitration cycle signal is an open collector signal whichindicates that a module is using the bus for more than one transfercycle (FIFO transfers). Bus busy is negated at the beginning of the lasttransfer cycle of a transaction to allow arbitration to be completedprior to the next available transfer cycle.

Transfer cycle signals, on the other hand, are comprised generally offour types: (1) information transfer, (2) information transfer parity,(3) module address, and (4) module address parity. The informationtransfer signals include eight, bidirectional tristate signals used totransferring information between modules, while the information transferparity signal is a tristate parity signal for the byte of data sent bythe information transfer lines, odd parity being used and examined forevery transfer cycle. The module address signals comprised four bitsused to note by the CPM 500 of the address of the interrupting IPM 502or to notify a IPM 502 that the current LMU bus transaction is for thatparticular IPM 502. This address must match the physical address. Itshould be noted at this juncture that module address parity signal isodd parity for the whole byte written into the address out register.

Two types of status signals are utilized according to the presentinvention. That is, an acknowledge (ACK) signal indicates that atransfer was received with good parity. The slave module always returnsstatus to the master module for out bottom transfers. If that parity isdetected, the ACK signal is not asserted. The other type of statussignal is a module busy signal which indicates that a transfer was notaccepted since the destination input buffer was full and the informationcould not be accepted.

General control signals consist essentially of four megahertz systemclocks, eight megahertz system clocks, physical address signals, the CPMRequest, the IPM Request, IPM data available, CPM data available, and amaster reset signal. Both system clock signals originate on the IPM, andare distributed evenly on the back plane. The physical address signalsdefine the back plane slot address within the unit of with the installedmodule providing the pull up for all physical address signals. Asdiscussed herein above, the CPM Request signal indicates that the CPM500 is sending one byte of information to the IPM 502 along with theaddress of a IPM 502. Likewise, the IPM Request signal indicates thatthe IPM 502 is sending one byte of information to the CPM 500 along withthe address of the IPM 502, to indicate the source of the interrupt. TheIPM data available (IPM DAV) signal indicates that valid information isbeing transferred from the IPM 502 to the CPM 500 on the LMU bus 504during a FIFO transfer operation. A maximum of 512 bytes of data can betransferred in one transaction, with the data being directed to theinput FIFO of the destination module. As long as this signal isasserted, a new byte of information is available for each megahertzclock cycle. In a similar manner, the CPM data available (CPM DAV)signal indicates that valid information is being transferred from theCPM 500 to the IPM 502 on the LMU bus 504 during a FIFO transferoperation. Driven from the CPM 500, the master reset resets all IPMs 502in the LMU 106. This signal is asserted when a power up reset or theprogrammable IPM reset in the CPM 500 is asserted.

As explained herein above with reference to FIG. 23, the IPM 502provides attachment to the LMU bus 504, a IBM 3270 compatible device(through a 3274/6 host computer terminal controller 104), and the LMUauxiliary bus 506. The IPM 502 has access to three external interfaces:(1) the LMU bus interface 524a, (2) the auxiliary bus interface, and (3)a 3270 communications interface 600. The LMU bus interface 524a providesthe IPM 502 with capability of communicating with the CPM 500 over theLMU bus 504. On the other hand, the auxiliary bus interface provides theIPM 502 with the capability of communicating with the CPM 500 on the lowband with serial auxiliary bus 506. This bus is used duringinitialization and diagnostics and is not used for functional operation.As such, the IPM 502 is a slave on this bus and cannot initiatecommunication until use is granted by the CPM 500. The 3270communications interface 600 provides the IPM 502 with the capability ofinterfacing to the host computer 108 through an IBM compatible 3270terminal controller. The IPM thus emulates a terminal in order to attachto a terminal controller.

Various diagnostic functions are available as part of the IPM 502hardware. For example, a IPM LMU bus buffer wrap allows the IPM 502 totransmit a request command from its LMU bus info out register to its LMUbus info in register. For this operation to work properly, the CPM LMUbus interface 524a must be disabled and the IPM LMU bus interface mustbe enabled. The destination address transmitted must be the address ofthe IPM 502. A IPM LMU bus FIFO wrap allows the IPM 502 to transmit datafrom the FIFO out to FIFI in. For this operation to work properly, theIPM LMU bus interface must be disabled. Data from the 3270 transmittermay be wrapped to the 3270 receiver through a 3270 interface wrap. Badparity can be forced into the FIFO out or info out registers byasserting the force bad parity bit in the IPM control register. Thiswill result in a parity error being detected when reading FIFO end orinfo in after a wrap operation is completed. Furthermore, a 3270receiver parity error detector can be checked by writing status thatcontains bad parity in the parity bit location for the first eight bits.After the status is written, a 3270 interface wrap is executed and thestatus is read as data from the 3270 receiver. A parity error willoccur.

Referring now to FIG. 27, a block diagram of the interface processorwhich handles all communication between the host computer terminalcontroller 104 and the CPM 500 will be shown. At the heart of the IPM502 is an 8×305 microprocessor 602. The microprocessor 602 initializesand controls all function within the interface, and transfersinformation between the 3270 interface and screen memory. Such amicroprocessor 602 provides direct addressing of program memory, pagedaddressing of data memory, direct addressing of external registers, aneight-bit data path, and an instruction execution rate of fourmegahertz. The interface vector bus (IV bus) is internal to the IPM 502and consists of those signals necessary to transmit data between themicroprocessor 602 and other logic on the IPM 502. Program memoryconsists of a PROM 604 that retains its contents when powered off. ThePROM 604 may be suitably implemented using 2K×8 programmable read onlymemories to provide a word-wide memory. Parity is not used, but the PROMcontent can be verified by a check some over its entire contents. Screenmemory 606 may be implemented using 4K×4 for static random accessmemories to provide a byte-wide memory, and is used to store informationabout the terminal screen being emulated by the IPM 502. Screen memory606 is on the IV bus, and since that bus can only address 256 bytes, apage register 610K is used to allow access to all four kilobytes ofscreen memory. IPM external registers 610 are addressed withinput/output addresses, and are shown in FIG. 28. Parity is only checkedwhen reading the 3270 receiver data 610e, FIFO in 610g, and IPM bus infoin 610c external registers.

The IPM 502 is reset by asserting either power up reset or IPM reset.Either reset being asserted initializes the microprocessor 602 andresets all interfaces on the IPM 502. FIG. 41 also indicates whichregisters are reset by -RESET. The microprocessor 602 is initialized byforcing it to begin program execution at program memory location 0000.

An 8×310 interrupt compressor 612 is utilized in conjunction with themicroprocessor 602, and allows the processing of three levels ofinterrupts. A level 1 interrupt is used to alert the microprocessor 602of a data byte at the 3270 receiver. Level 2 interrupts are reserved forfuture use. The lowest priority interrupts, level 3 interrupts, are usedto indicate a group of interrupts available through the interruptcontroller in the MK3801 614. As shown in FIG. 29, level 3 interruptsincludes 16 different interrupts ranked in priority from highest tolowest.

The IPM external registers 610 are used to identify and indicate variousconditions within the LMU 106. For example, as shown in FIG. 30a, aphysical address register 610a is used to identify the physical positionof a module in the LMU 106. Status of logic on the IPM 502 is identifiedin an IPM status register 610b (FIG. 30b). A LMU bus in register 616ccontains a byte of data received over the LMU bus 504 when CPM Requestis asserted. The byte of data accessed from the MK 3801 STI is containedwith a STI data register 616d which must be accessed from the STI forthe register 616d contains valid data. Either data received over the3270 serial port or status collected internally by the 3270 receiver iscontained within a 3270 receiver data register 616e. The data that isaccessed is determined by the 3270 stat/data cell bit in the 3270control register.

Referring now to FIG. 30c a 3270 external status register 610f is shown.When bit 7 is asserted, the 3270 byte of data previously read was acommand byte. On the other hand, when bit 7 is negated, the 3270 byte ofdata previously read was a data byte. This bit must be examined aftereach data byte is read from the 3270 receiver. When bit 6 is asserted,the 3270 is receiving data from the serial port. This means that thereceiver has detected a valid start sequence and has not received avalid ending sequence. All information between the start and endingsequences is treated as valid data unless an error is detected. Bit 5,when asserted, is indicative of the 3270 receiver having detected anerror during the reception of data from the serial port. Bit 4 indicatesthat the transmitter cannot accept another byte of data until thecurrent byte is transmitted, and bit 3 indicates that the transmitter isready for, or is in the process of, transmitting data on the serialport. When asserted, bit 2 indicates a data byte is in the 3270 receiverholding register, and the assertion of bit 1 indicates a parity errorwas detected when data was read from the 3270 receiver holding register.

At the output stage of the input FIFO is a FIFO in register 610g. Eachtime a byte of data is read from the register 610g, the next byte ofdata is presented at the output of the FIFO until such time that theFIFO is empty.

A IPM control register 610h, which contains bits that control theoperation of the IPM 502 as its name implies, is shown in FIG. 30d. Bit6, when asserted, causes bad parity to be written into the FIFO out andinfo out registers, when accessed. When negated, good parity is writteninto such registers. The IPM request wrap (bit 4) causes the next IPMRequest transaction to be wrapped back to the IPM 502 as a CPM Requesttransaction. When asserted, bit 3 causes the next data transfer to bewrapped from the FIFO out to FIFO in.

The IPM 3270E enables/-Wrap (bit 2) when asserted causes the 3270receiver to be enabled to detect transmission over the 8570 interface.The coax driver is also enabled to allow transmission on the coax. Whenthis bit is negated, the 3270 transmitter and receiver are in the wrapmode. The receiver is disabled from the 3270 interface and detects datafrom the transmitter on the IPM 502. The transmitter will only send datato the IPM receiver and not on the coax. Bit 1 when asserted will causethe IPM 502 to assert the IPM Request signal on the LMU bus 504 during atransaction. The IPM 502 will also output a single byte of informationfrom the LMU bus info out register along with its address. When a zerois asserted, the IPM 502 will arbitrate for the LMU bus 504 and, uponbecoming bus master, will transfer data from the output FIFO to the LMUbus 504 until the FIFO is empty. The output FIFO must be loaded with thedata tot be transferred before the bit is sent.

Referring now to FIG. 30e, an IPM enable register 610i is shown. Whenasserted, bit 7 enables the auxiliary bus drivers. The auxiliary busreceivers are always enabled. Bit 6, when asserted, enables the LMU businterface drivers and receivers. The IP indicators (bits 3-0) controlthe IP indicator light emitting diodes on the edge of the IPM board.When these bits are asserted, the light emitting diodes are turned on,and when negated turned off. An LMU bus info out register 610j may beloaded with data to be transferred to a destination on the LMU bus 504when the IPM interrupt signal is asserted on the LMU bus 504. As shownin FIG. 30f the screened memory page register 610k selects one of 16,256-byte pages of screen memory.

A STI address register 610m contains bits that address the internalregisters of the MK 3801, selecting those registers and controlling theM1 bit. At the same time, a STI data register 610n is used to load theaddress register in the MK 3801 (FIG. 27), while a STI control register610o contains bits that control the internal operations of the MK 3801as will be explained in detail herein below. A FIFO out register 610pcomprises the first stage of the output FIFO. As data is written intothis register, it is stored in successive locations on the FIFO untilsuch time that the FIFO is full. Writing to a 3270 transmitter dataregister 610q loads information, either data or status, into the 3270transmitter. If data is to be loaded, the 3270 stat/data bit must benegated in the 3270 status register. If status is to be loaded, the 3270stat/data bit must be asserted. Before status is loaded into the 3270data register 610q, the 3270 status register must be loaded.

A 3270 control register 610r, as its name implies, contains bits thatcontrol the operation of the 3270 receiver and transmitter. Whenasserted, one bit of the register 610r causes the 3270 transmitter toreturn clean status on the serial link without loading any otherregisters. Bit 6, when asserted, indicates that operations with the 3270transmitter or receiver will involve status. This means that status willbe written to the transmitter or read from the receiver. When this bitis negated, operations with the transmitter or receiver will involvedata. Data can be written to the transmitter or read from the receiver.Bit 5 is the 3270 status bit 10 that will be written to the 3270transmitter with a write 3270 data operation. In order to write bit 5,bit 6 must be asserted. Bit 4 is the 3270 status bit 11 that will bewritten to the 3270 transmitter with a write 3270 data operation. As inbit 5, bit 6 must be asserted to write bit 4.

Two pseudo registers may also be used. A reset parity error register610s, when written to, resets the FIFO in, bus in, and 3270 parity errorflags. No data is required during the write register 610s. The reset busstatus register 610t is a pseudo register that, when written, resets theerror flags for LMU bus NACK, module busy, and LMU bus parity error.Like the reset parity error register 610s, no data is required duringthe write to the reset bus status register 610t.

In order to provide the IPM 502 with additional interrupt handling andtimers 506, a serial time interrupt (STI) controller such as the modelMK3801 manufactured by Mostek is implemented with the IMP 502 of thepresent invention. With reference now to FIG. 31 which shows a blockdiagram of the STI controller 618, the following examples depict thenecessary sequencing for use of the STI controller 618. In order towrite to an STI internal register, the STI address register 618a must beloaded with the address of the desired internal register. Thereafter,the STI data register 618b is loaded with data to be loaded into theinternal register. A STI control register 618c subsequently asserts thennegates WR and CE signals to the STI controller 618. The STI 618 musthave the WR and CE signals negated at least two cycles betweensuccessive operations.

In order to read a STI internal register, the STI address register 618ais loaded with the address of the desired internal register. Then theSTI control register 618c asserts RD and CE, STI data is read from a STIread buffer 618d, and the RD and CE signals are negated in the STIcontrol register 618c.

The IPM interface 620 to the LMU bus 504, as shown in FIG. 30 allowsfull access and use of the entire LMU bus 504 which provides acommunication path between the CPM 500 and the IPM 502.

The LMU operator's panel, as shown in FIG. 33, provides switches andindicators to control and observe the operation of the LMU 102. Theoperator's panel contains functions exposed to the operator, andfunctions behind the covert available to a field engineer, and iscontrolled by the CPM 500 through the operator's panel interface 524f.Operator accessible functions include a DC power on/off switch 622comprising an alternate actions which, when depressed on one side,closes DC power to be applied to LMU 102, and who moves such power whento press to the other side. DC power on/off indicator 624 eliminateswhen DC power is on, and is extinguished when power is off. The IPLcomplete indicator 626 is a light emitting diode which eliminates toindicate that the initial program load process has been completed. Alight emitting diode indicator is also used as a LMU check 628 which,when eliminated, indicates the occurrence of a hardware detected error.A 4-character, alpha numeric display 630 contains additional informationas to the nature of the error, and is used to indicate error codes usedin utilizing in analyzing the state of the LMU 102. Field engineeringaccess all functions include a conventional RS-232C connector forattachment of a maintenance device, the CPM resets which, and the CPMIPL switch.

A non-volatile random access memory (NVRAM) may be installed on eachfield replaceable unit to allow the microprocessor 518 to accessinformation on any field replaceable unit within the LMU 106. The NVRAMcan store 16-words of information, with each word 16-bits in length. A4-word interface, from the CPM 500 to all field replaceable unit IDMVRAM s allows the microprocessor 518 to access the information. MFRUclock signal from the CPM FRU ID register controls the clocking of thedata to or from each MVRAM. Data in and data out signals carry datarespectively from the CPM FRU ID register to the MVRAM and from theMVRAM to the CPM status register. A separate select signal for eachMVRAM, originated from the CPM FRU ID register, selects a particularMVRAM when asserted for communication with the microprocessor 518.

Having described the LMU 106 in some detail, the following will explainthe requirements for interfaces within the LSM 108, the LMU 106, itsassociated software, and operating procedures. As explained hereinabove, the REI 156 is the communications path between the LCU 109 andthe electronics which are mounted on the arm assembly portion 138. Thispath must provide a means of reading and writing of registers on the armelectronics, transfer of camera data, and power to the arm electronics.Three basic signal connections for the REI 156 comprise a parallelcommand signal, a camera DMA signal, and a reset signal. The parallelcommand signal is the read/write communication path between the LCU 109and the arm assembly portion 138. The serial command signal pathinitiates the transfer of data from the camera 310, the path from whichthe camera data takes from the arm assembly portion 138 to the LCU 154comprising the camera DMA signal. The reset signal is a hardwiredconnection between the LCU 154 and all electronics on the arm assemblyportion 138. When active, all arm electronics will be sent to a knownstate and a dynamic brake relay 630 will stop all motion. Power is stillapplied to the arm electronics when reset is active. The reset signal isset and reset by the microprocessor 618. If the REI reset signal path isbroken, the arm electronics will be reset and a status bit sent toindicate a broken connection.

A detached diagnostics device 632 can be attached to the LSM diagnosticport which may be suitably comprised of a conventional RS-232 port.Diagnostics can thereafter be performed on any LSM 108, not just the LSM108 to which the detached diagnostics device 632 is attached. Softwarecontained with the LCU 109 for, as will be explained herein below,converts the RS-232 message into the appropriate LSM message. The LMU106 then sends the executable diagnostic to the specify LSM 108, andsends any screen responses to the LSM 108 to which the detacheddiagnostics device 632 is attacked. The detached diagnostics device 632must be used to place the LSM 108 in a maintenance mode which requiresthe LSM 108 to be off line from the host computer 108, beforediagnostics may be run.

A camera DMA interface 634 may be suitably used to provide a dedicatedserial link between the LCU CDI logic 636 and the wrist CDI logic 638.Data received from the camera array 310 is the only informationtransferred across this link, always going from the wrist CDI logic 638to the LCU CDI logic 636 over the REI serial command path.

Functional operation of the LSM 108 and optimization programs whichreside in the LMU 106 necessitate the use of a tape unit interface.Commands from the LCU 109 to the tape unit 152, as follows, are at leasttransferred across the tape unit interface:

TU REWIND/UNLOAD

RESET TAPE DRIVE

HOLD OFF LOAD

RESET HOLD OFF LOAD

SENSE

BLANK DISPLAY

Also transferred across the tape unit interface are at least thefollowing tape unit status indications:

TD ACCEPTED THE LIBRARY COMMAND

TD REWINDING

CARTRIDGE PRESENT

CARTRIDGE LOADED

TD READY

TD READY SWITCH

OFF LINE

ESTIMATED TIME TO UNLOAD

CARTRIDGE TRAY UP

CARTRIDGE TRAY DOWN

MACHINE CHECK

LOAD CHECK

CLEANING NEEDED

MANUAL INTERVENTION REQUIRED

Four other interfaces are required to complete communication among theACS 100: (1) an LSM operator panel interface 642, (2) a cartridge accessport interface 644, (3) a power supply interface 646, and (4) a thetaarm interface 648. The LSM operator panel interface 642 is required foroperator communication with the LSM 108, the protocol for which is asubset processor data bus interface 636 consisting of data/address bitsand minimal control lines. The cartridge access port interface isrequired for LCU communication with the cartridge access ports. Protocolfor the cartridge access port interface 644 is also a subset of theprocessor data bus interface 636 consisting of data/address bus bits andminimal control lines for support of multiple cartridge access portconfigurations. Early power failure warning and power supply marginingare provided across the power supply interface 646. As in the LSMoperator panel interface 642 and the cartridge access port interface644, the protocol for the power supply interface 646 is a subset of theprocessor data but interface 636 consisting of data/address bus bits andminimal control lines. Finally, the theta arm interface 648 provides themeans by which the LCU 109 can deliver commands for movement of thetheta arm 142.

Interface requirements between the host computer 102 and the remainderof the ACS 100, through the LMU 106 will now be described. The LMU 106communicates with the host computer 102 by attaching to a conventionalterminal control unit 104 and emulating a 3270 type terminal. The LMU106 is, therefore, capable of supporting attachment to IBM 3270 forcontrol unit models 21B, 21D, and 31D, which in turn support 360/370channel attachment.

Transfer of data from the terminal control unit 104 to the LMU 106begins with the terminal control unit 104 issuing a "load addresscounter high and low" command as shown in FIG. 34. All commands receiveda transmission turn around/auto response (TT/AR) indicating receipt ofthe data without error. The screen address set in the load addresscounter high and low must be row zero at column zero, thus providing aconsistent address and allowing the LMU 106 to ignore local control unitto terminal writes. The actual request data is transferred with the"write data" command.

Data is transferred to the terminal control unit by emulating successivekeyboard strokes with an "enter" key at the end as shown in FIG. 35. Thepoll command is used to retrieve each data byte and the poll/acknowledgecommand is used to acknowledge each byte.

The host to LMU protocol is used for content or informational transferbetween the host computer 102 and the LMU 106. With such protocol, thehost computer 102 initiates action of the LMU 106, and the LMU 106returns status back to the host computer 102. This host to LMU protocolassumes the basic means of data transfer is accomplished by the 3274 LMUprotocol.

Basic transmission types are requests, response, and messages, plusmessage acknowledgments and error responses. A transaction consistsgenerally of a start of transaction, the length count, the sequencenumber, the transaction type, the actual data, and an end oftransaction. Requests are used by the host computer 102 to initiateaction within the LMU 106. The request data contains a unique requestcode and any additional parameters needed to specify the host request.Responses are returned to the host computer 102 as a reply to a hostrequest. They contain a unique response code that correlates back to therequest, and any additional required data. An intermediate response typeindicates that a portion of the host request has been satisfied but thatadditional responses will be returned for that request. A final responsetype indicates that the request is finished and no further responseswill be returned. The sequence number, contained in the responsetransactions, is always identical to the sequence number contained inthe original request transaction.

For a request failure, an error response is returned to the hostcomputer 102 instead of the normal response. This response contains thesequence number of the original request, and no further responses arereturned on the request. The error response contains enough informationto assist in isolating a failing field replaceable unit for hard errors,and may also assist in host software error recovery procedures.

Messages are unsolicited transmissions from the LMU 106 to the hostcomputer 102. Messages contain a unique message code identifier, andindicate asynchronous events occurring within the ACS 100. Messages arecomprised generally of two basic types: (1) a message ACK required, and(2) a no message ACK required. Messages of the "message ACK required"type are retained in the LMU 102 until a message ACK transaction isreturned to the LMU 102 from at least one interface. If an interface isbroken, an initial attempt will not be made to send the message to thatinterface. If all interfaces are down, the LMU 106 will retain themessage until it can be sent and acknowledged across a workinginterface. Messages of the "no message ACK required" type require noacknowledgment from a host computer 102. The LMU 106 attempts to sendmessages to all working interfaces. If an interface is broken, themessage is discarded for that interface. A message acknowledgment issent from the host computer 102 to the LMU 106 to indicate that themessage has been received by the host computer 102. As discussed hereinabove, the sequence number contained in the transaction is that of theoriginal message.

If the LMU 106 has multiple requests active at any given time, they willnot necessarily be executed in the order received. Due to internaloptimization and resource contention, the order of execution may vary.If the order of execution is critical, the host computer 102 must waitfor completion of one request before issuing another.

In general, requests are retried internally in the LMU 102 beforereturning the error response. If the host computer 108 desires to retrythe request, it does so by reissuing the prior request that failed. Thenumber of retries is not limited by the interface, but is determined bythe error recovery procedures if the host computer 108 receives aresponse containing an error, it can reissue the original request forretry. In the event that a host computer 102 desires to assumeresponsibility for another host computer 102 (cross-host recovery), a"assume alternate host communication" request can be issued to assumethe activity of the other host computer 102. Any outstanding activitycan then be continued with the assuming host computer 102. The hostcomputer interface 650 supports controlling the state of an LSM 108 inone of two defined states: (1) off line, and (2) on line. In the offline state, the host computer 102 is not allowed to issue any requeststo that component except for a request to change the state to on line.The host computer 108, in the on line state, is allowed to issue anyvalid request to the component.

A state change made from one host computer 102 is reflected on all hostcomputers 102. The state of an LSM 108 never varies from one hostcomputer 102 to another. In general, if an LSM 108 is off line, allnormal requests will be rejected. Communications between the hostcomputer 102 and the LMU 106 relating to the change of state of an LSM108 are of two types. A "vary LSM request" contains a LSM ID, andmodifier which may be issued and accepted regardless of the current LSMstate. Modifiers consist of "on line" which requests a transition to theon line state, "off line" which requests a transition to pending offline if requests are outstanding on the LSM 108, and "off line force"which requests a transition to off line immediately without regard toany outstanding requests on the LSM 108. With the "on line" modifier,the LSM 104 will go on line only if it is available for functionaloperation. The "off line" modifier can cause a transition to off line ifno requests on the LSM 108 are outstanding. Once in a pending off linestate, the LSM 108 goes to off line when all requests are completed.When off line, all mechanical motion in the LSM 104 it is stopped. If a"vary LSM request--on line--" is received before the outstandingrequests are completed, the latter requests takes precedents and the LSM104 goes back on line. With the "off line force" modifier, anyoutstanding requests for the LSM 108 are not preserved.

A "vary LSM response" is returned when the LSM 108 goes to the on lineor off line pending, or off line state. The current state is returned tothe host computer 102. If another "vary LSM request" is issued before aprevious "vary LSM request" has returned its response, the prior requeststill returns a response (with the original sequence number), butindicates that the request was overridden. If a cartridge access portrequest is still outstanding, the LSM 108 will not go off line inresponse to a "vary LSM--off line" request. The enter or eject state ofthe LSM 108 can be ascertained by issuing the LSM status request. If anLSM 108 enters the off line state, any previously existing cartridgeaccess port reservations are released.

The following describes the communications required for movement ofcartridges within the ACS 100. A "mount" request contains a modifierbyte, VOLSER, source cell address and LSM ID, the destination drive IDand LSM ID which are used by the LMU 102 to take a tape cartridge 286from a cell and mount the tape on a drive 150. The modifier indicatesthat the visual cartridge label compares to the VOLSER, verifies thatthe label cannot be read, that a label check is to be completely bypass,or that only a recovery cartridge number is specified. With the secondand third options, above, no attempt is made to compare the VOLSERcharacters with the actual label on the cartridge, the VOLSER charactersbeing retained internally as a token for recovery purposes only. Use ofthe last option means that a recovery cartridge number is contained inthe VOLSER field. The source modifier specifies that either a normalcell source is specified, or that the source is an "in-transit" locationdue to a prior failure. In response to a "mount" request, a mountresponse acknowledges when the cartridge 286 has been mounted andreadied on the drive 150. The number of LSMs 108, used in the cartridgemove, (excluding the source LSM), is returned in the response. Thisrequest can be issued while a single dismount for the same drive 150 ispending to complete a prior rewind and unload. Recovery of any cartridgemovement is possible by using any move request in conjunction with aread transition cartridge request. Host recovery is required when eithera major LMU or LSM failure occurs. When an LMU ready message isreturned, it indicates that lMU 102 has just powered or received a resetand host recovery is required. When an LSM not ready message isreturned, followed by an LSM ready message, host recovery is alsorequired.

The host computer 102, detecting that cartridge recovery is required,issues a read transition cartridges request. This returns a list ofcartridges in an "in-transit" location, which could be passed throughports-or hands. A mount, dismount, swap, or move request can, then beissued against this list of cartridges. For all "in-transit" cartridges,the source modifier should be sent to "in-transit". For cartridges thathad a readable VOLSER, the "verify VOLSER label" modifier should bespecified for cartridges in which the label was unreadable, and thetoken volser was retained and returned under the read transitioncartridges request, either the bypass label or verify unlabeled optioncan be used. All other cartridges, for which no VOLSER data isavailable, must use the recovery cartridge number modifier. The LMU 106will correlate the recovery move requests with an internally maintainedcartridge list to identify the correct cartridge for movement. FIGS. 36aand 36b illustrate respectively, a mount request and a mount response,while FIG. 36c and 36d is a flow chart of the actions taken by the ACS100.

Referring now to FIG. 37a and 37b, communications required to dismount acartridge will be described. A "dismount" request, contains a labelmodifier, a source modifier, volser, source drive ID and LSM ID, thedestination cell address and LSM ID which are used by the LMU 106 toremove a tape cartridge 286 from a drive 150 and move it to a cell 132.The label modifier and source modifier are described herein above withreference to the mount section. A "dismount" request issues a rewind andunload to the drive 150 only if instructed by the host software. Inresponse to the "dismount" request, a "dismount" response acknowledgeswhen the cartridge 286 has been dismounted and moved to the destinationcell 132. The number of LSMs 108, used in the cartridge move (excludingthe source LSM), is returned in the response.

"Swap" requests and responses, that is communications required to move acartridge from one drive 150 to another, will now be described withreference to FIG. 38a and 38b. A "swap" request contains a labelmodifier, source modifier, VOLSER, source drive ID and LSM ID, and thedestination drive ID and LSM ID. The "swap" request moves a tapecartridge 286 from one tape drive 150 directly to another- tape drive arewind and unload to the drive 150 only if instructed by the hostsoftware. In response to the "swap", the "swap" response is returnedwhen the cartridge 286 has been mounted on the destination drive 150.The number of LSMs 108, used in the cartridge move (excluding the sourceLSM) is returned in the response. A flow chart of the actions taken bythe ACS 100 is shown in FIG. 38c.

In order to change cell locations of a cartridge 286, a "move" requestis used. As shown in FIGS. 39a and 39b, the request moves cartridgesbetween ordinary cells 132 and cartridge access ports, with movements toor from the cartridge access port only being done when the enter oreject mode is active on the same host computer 108. The "move" requestcontains a label modifier, source modifier, a VOLSER, source celladdress and LSM ID, and a destination cell address and LSM ID. Inresponse thereto, the "move" response is returned when the cartridge 286has been moved to the destination cell 132. The number of LSMs 108, usedin the cartridge move (excluding the source LSM), is returned in theresponse. A flow chart of the actions taken by the ACS 100 is shown inFIG. 39c.

As previously described, the cartridge access port consists of a cellarray of a plurality of cell locations that are directly accessible tothe robotic means 140. Additionally, the operator has access to suchcartridge cells via the access door that on the outside of the LSM 108.The cartridge access port is capable of excluding access by the roboticmeans 140 when the operator is accessing the cartridges and vice versa.The following describes the interface of entering and ejectingcartridges with the cartridge access port.

All cartridge access port operations are bracketed with the reserve andrelease CAP requests. CAP reservation during a "vary LSM off line" stateis described herein above with reference to the vary LSM request. A"reserve CAP request" contains the LSM ID of a specific cartridge accessport, after which the cartridge access port becomes reserved to thecurrent host computer 102 for enter or eject operations until a "releaseCAP request" is issued. In response thereto, a "reserve CAP response" isreturned if the LMU 106 is able to establish the requested reservation.The cartridge access port must be operational and not reserved from anyprior request. If another host computer 102 has the cartridge accessport reserved, the ID of that host computer 102 is returned in the errorresponse. A "release CAP request" contains the LSM ID of a specificcartridge access port, and causes the cartridge access port to becomereleased from the current host computer 102. In response thereto, a"release CAP response" is returned when the LMU 106 ends the currentreservation of the host computer 102. With one exception, no requestswith the cartridge access port can be outstanding for this response tobe returned. The exception is if an enter request has been issued butthe cartridge access port door has not yet been open to enter anycartridges. In this specific case, the release CAP request will behonored.

Once reservation of the cartridge access port is established, eitherenter or eject requests can be issued. Although enter and eject requestscan be mixed, it may be desirable to limit the cartridge movement toonly one type at any time. The enter/eject requests and move requeststhat address the cartridge access port are rejected if the issuing hostcomputer 108 does not have reservation of the cartridge access port.

Enter operations consist of the following communications. An "enterrequest" contains a recovery modifier and the LSM ID of the desiredcartridge access port, causing the door to be unlocked and the "entercartridges" light to be turned on. Under one recovery option, thecartridge access port door must be closed and locked in order for therequest to be accepted. With the cartridge access port reserved to thehost computer for such request to be accepted. The operator then canenter the cartridges 286 for which a number of responses may be made. A"CAP door opened response" is returned, as is apparent, when thecartridge access door is opened. Likewise, a "CAP door closed response"is returned when the CAP door is closed and causes the door to beautomatically locked. The "enter cartridges" light is turned off at suchtime. Once the cartridge port door is locked, the ACS 100 proceeds toreport the status of the CAP cells by using a "CAP catalog response".This response contains the status of the CAP cells of the LSM 104. Foreach cell, the cell status and volser (if available) are returned, withthe information being returned in the same order that the cells arenumbered. Cell status indicates whether a readable volser was found, andunreadable was found, or no cartridge was found. When an enter operationis prematurely terminated by a "release CAP request", a "enteroperations terminated response" is returned. This can occur only when anenter request has been issued, but no door opening event has beendetected.

As explained herein above, the host computer 102 moves the cartridges286 out of the cartridge access port by using either a move or mountrequests. There responses must be returned before other requests can beissued to the cartridge access port. Successive enter operations arecontinued by repeating the enter and move requests. If cartridges areentered that are unacceptable to the host computer 102 (i.e.,unreadable), the host computer 102 can reject those cartridges 286 byforegoing the move request and issue the enter or eject requests. Oncethe cartridges 286 are removed, the host computer 102 can continue withnormal enter operations. A flow chart of an "enter" operation is shownin FIG. 40.

Eject operations also occur within the bracketing of a reservation andconsists of the following communications. An "eject request" contains arecovery modifier and the LSM ID of the desired cartridge access port.It turns on the "eject cartridges" light and enables ejection byunlocking the door. In all other aspects, this request is identical tothe "enter requests". The CAP door open, the CAP door closed, and theCAP catalog responses are returned in response to the eject request, theCAP catalog response being returned to indicate that all cartridges wereejected. All cells should have a "no cartridge found" status. Cartridgesthat the operator inadvertently left in the cartridge access port can beejected by reissuing the eject request.

For a major failure of the LSM 108, the host computer 102 should firstissue the read transition cartridges request as required under thegeneral cartridge recovery scenario. The host computer 102 should issuethe LSM status request to determine if the cartridge access port iscurrently reserved. If reserved, the host computer while holding thereservation should perform the recovery. If it is desired that anotherhost computer 102 assume CAP recovery, the assume alternate hostcommunications request should be used. If no host reservation exists,then any host computer 102 can reserve the cartridge access port andperform recovery. The LSM status response also returns the status of thecartridge access port.

If enter or eject requests were issued with the cartridge access portdoor closed at the time of failure, no special recovery of thoserequests is needed. However, if the cartridge access port door is open,either the enter or eject request should be issued specifying therecovery option. Receiving either of the requests allows the request tobe started at the point of waiting for the door to be closed. Theoperator can then take the appropriate action to enter or ejectcartridges and then close the door. CAP door closed and CAP catalogresponses are returned to the host computer 102.

With the cartridge access port closed, any cartridges in transition toor from the cartridge access port can now be recovered by issuing anymotion request with the recovery option. From an interface viewpoint,any normal request can now be issued to continue any other cartridgeaccess port recovery. This should include issuing a catalog request ofthe cartridge access port. Any cartridges remaining in the cartridgeaccess point should be moved into the LSM 108 via normal moves, orejected via the eject request.

Referring now to FIGS. 41a and 41b, catalog requests and responses willbe described. A "catalog request" contains an LSM ID, an optionspecifying to catalog either a full panel, subpanels (cells within apanel), cartridge access ports or drives, and a range specifying thebeginning and ending positions. This request only initiates thecataloging of a single LSM 108.

For a full panel, a beginning and ending panel number is specified. Norow or column address can be specified as the entire panel is cataloged.The catalog response for a panel proceeds sequentially across the firstrow from one column to the last. It then proceeds down to the next rowof the panel in the same manner until all rows have been cataloged.

For the subpanel option, a cell or cells 132 within a single panel canbe cataloged. The beginning address specifies the panel and thebeginning and column address. The ending address specifies the endingrow in column. An ending panel number is not used. The order of thecatalog response is to start the beginning row, proceeding sequentiallyacross all columns until the ending column is reached. It then proceedsdown to the next row and again catalogs from the beginning to the endingcolumn until the ending row has been cataloged. The ending column mustbe greater than, or equal to the beginning column.

Cartridge access port cataloging can be performed only when the CAP isreserved and the door must be closed. For drive cataloging, a simplescalar range is specified. Cataloging of the drive cartridges is limitedonly to cartridges that are unloaded.

In response to the "catalog request", the "catalog response", as shownin FIG. 41b contains the status of the requested cells 132 of the LSM108. For each cell 132, the cell status and VOLSER (if available) arereturned. The cell status indicates whether a readable VOLSER was found,an unreadable VOlSER was found, no cartridge was found, or no cellexisted at this position. The catalog response proceeds through thespecified range as described under the catalog request. All potentialpositions are cataloged even when occupied by cartridge access ports orpass through ports. If a major failure occurs during a "catalogrequest", the host computer 102 should determine what positions remaineduncataloged and reissued the request with the new range.

The host computer 102 may also verify LMU/LSM configuration. A "readconfiguration" request initiates the configuration response, whichreturns the sequence number and the configuration of the ACS 100including the types of panels within a LSM 108 and pass through portconnectivity. A capability also exists to group several interfaces intoone logical group, thus allowing alternate pathing when an interfacefails. Such pathing is implemented by a "set host path group request"which contains a host identifier and a modifier to join, resign, ordisband the current interface with the host identifier group. A "sethost path group response" indicates that the LMU 106 has established thedesired host path group.

Various messages, that is, transmissions to the host computer 102 thatare unsolicited by a request, are also provided in accordance with oneimportant aspect of the invention. With the exception of a "door opened"message, all messages require no acknowledgment. An "error message"contains information that describes errors within the ACS 100. It isused when an error occurs without causing a request to fail. A"host-to-host message" returns data to other host computers 102.

Other transmissions to the host computer 102 that are unsolicitedcommunicate various equipment status. For example, a "door open message"returns the LSM ID of the door that opened. This event is preserved upona loss of LMU or LSM power until a message acknowledgment is received.In response to the "door open message" a "door open messageacknowledgment" indicates that the host computer 108 has received the"door open" message. A "door closed message" returns the LSM ID of thedoor that closed. No acknowledgment is necessary. A "LSM ready message"returns the LSM ID that becomes ready, indicating that the LSM 104 hasbeen powered on, has been initialized for functional use, and is not inmaintenance. This message is returned regardless of the off line/on linestate. A "LSM not ready message" returns the LSM ID that becomes notready, indicating that the LSM 104 has become inoperative. This messageto is returned regardless of the off line/on line state. A "LMU readymessage" returns the LMU ID that becomes ready, indicating that the LMU102 has been powered on, has been initialized for functional use, and isnot in maintenance mode.

In accordance with another important aspect of the invention,performance monitoring of the ACS 100 is possible through a "ACSstatistics request" and a "ACS statistics response". The statistics onceread can be reset, and include a percentage of arm utilization and passthrough counts for each LSM 104. The time of day, included in theresponse, indicates the beginning of the monitoring (time at whichstatistics were reset) as per the LMU time of day clock.

Other communications between the host computer 102 and LMU 106 are usedfor control. For example, a "message route request" includes a messageto be routed to all other host computers 102. This request relies on theconfiguration set up by the "set host path group request". In responseto a "message route request", a "message route response" returns a listof host IDs to which the message was successfully routed.

An "assume alternate host communications request" contains an alternatehost ID and allows the issuing host computer 102 to receive all messagesor responses destined for another host computer 102. The alternate hostID is the one originally set from the other host computer 102 using the"et host path group request". Only the current, or queued, requests inthe LMU 106 are switches to the assuming host computer 102. Any newrequests issued over the other host computer 102 will have thereresponses return to the other host computer 102. This requests issuedover the other host computer 102 will have their responses returned tothe other host computer 102. This request does not cause the hostinterface grouping of the issuing or other host computer 102 to bechanged. Additionally, any CAP reservation established to the other hostcomputer 102 may be broken and continued on the assuming host computer102 by such request. A "set alternate host communications response"returns data pertaining to each request that was assuming from thealternate host computer 102.

A "read transition cartridges request" specifies an LSM 108 for whichrecovery is required. The targeted LSM 108 must, as a conditionprecedent, be currently in the ready state. In response to such request,a "transition cartridges response" contains a list of cartridges thatwere found in transition upon a power-up of a LSM 108, LMU 106, or both.As explained herein above, a cartridge is defined to be in transitionwhen found in the hand and finger assembly 236, or in a pass throughport. For each cartridge 286, the label status and label are returned,indicating a readable label was obtained, and unreadable label was foundbut the token VOLSER originally issued with the request was preserved,or an unreadable label was found but no token VOLSER was preserved. Inthe latter case, the LMU 106 assigns a recovery cartridge number to thecartridge 286 for subsequent identification purposes. This number isthen placed in the VOLSER field. Finally, requests and responses areavailable in accordance with the present invention to obtain the statusof various portions of the LSM 108 or LMU 106.

Two levels of communication between the LMU 106 and a LSM 108 aregenerally utilized in accordance with the present invention. The first,microcommunications, involves the actual transmission of data withoutregard to its content. Checking is done at this level for cleantransmission of data (e.g., parity, CRC checking) only. The meaning ofthe transmission is ignored. The transmission is initiated from the LMU106 or the LSM 108 having knowledge by the recipient.

All transmissions and acknowledgements contain the followinginformation: (1) recipient identifier, (2) sender identifier, (3) packettype, (4) sequence number, and (5) data. The sequence number is atransmission identifier generated by the originator of the transmissionand is used to link the transmission with the acknowledgement. Packettypes include: (a) Acknowledge good receipt, (b) No acknowledge (badreceipt), (c) Poll (from LMU), (d) Command (from LMU), (e) Response(from LSM), (f) Message (from LSM), (g) Diagnostic command (from LMU),and (h) Diagnostic response (from LSM). The data field contains specificinformation (microcommunications) indicating the kind of command,response or message along with any modifiers necessary. No data field isincluded for POLLS, ACKs or NACKS since such communications exist at themicrocommunications level only.

The sender initiates the transmission and then waits for thetransmission acknowledgement. In a good acknowledgement, the recipientidentifier will be the same as the transmission sender identifier, thesender identifier will match the transmission recipient identifier. Thesequence number will equal the transmission sequence number, and thedata will be a "transmission acknowledgement". For example, a cleantransmission and acknowledgement of an LMU communication might occur asshown in FIG. 42.

Several things can happen that will disrupt a good transmissionsequence. For example, the recipient may receive a communication with atransmission error and respond with a transmission check. The recipientcould also not see a recognizable communication. The sender couldreceive a communication with a transmission error or not get arecognizable acknowledgement. In order to avoid lost transmissions, ormistaking multiple occurrences of the same transmissions as separatetransmissions, the following rules must be followed: All occurrences ofa transmission must have the same sequence number; a fixed maximumnumber of transmission re-tries will be made; and, if the sender doesnot receive a good transmission acknowledgement within a fixed period oftime, it will re-try the transmission.

The sender may not reuse a sequence number until it has received anacknowledgement for a communication with another sequence number. If therecipient receives a communication with a transmission error, it willrespond with a transmission check (No acknowledgement). Once therecipient receives a clean transmission and responds with a transmissionacknowledgement, it may take action on the transmission. After therecipient sends a transmission acknowledgement, it must store thesequence number until it receives and acknowledges a transmission withanother sequence number. If it gets more transmissions within thatperiod with the same sequence number, it will respond with atransmission acknowledgement but will take no further action on thattransmission.

A second level of communications between the LMU 106 and LSM 108,macrocommunications, are comprised of the content and meaning of thedata transmitted by means of the microcommunications. This informationis transferred in the data portion of the transmission. Generally, thereare three types of macrocommunications: (1) LSM commands, (2) LSMresponses, (3) LSM messages. LSM commands are commands issued by the LMU106 to the LSM 108 in the form of immediate or functional commands.Immediate commands are distinguished from the functional commands bynoting that only one functional command at a time will be processed,while more than one immediate command can be in process at a time. Thecommand is accepted on a micro-level when the LSM 104 returns atransmission acceptance, indicating a clean reception. A second type ofmacrocommunications is the LSM responses. These are responses tospecific a LSM commands issued by the LMU 106. They include commandrejection, and command ending status responses. If the command is eitherillegal or not currently executable by the LSM 108, a command rejectwill be issued by the LSM 108. Upon completion of the command, whethersuccessful or not, the LSM 108 will return command ending statusindicating the result of the execution of the command and/or anyrequested information.

If the LSM 108 chooses not to accept the command, the LSM 108 will issuea command rejection. Reasons for rejection include those listed underspecific commands as well as an inability to perform the command,function down-load required for the command, illegal block length,illegal parameter, or that a functional command is in progress.

Pieces of information which are transmitted from the LSM 108 to the LMU106 without any initiating action having been taken by the LMU 106 are athird form of macrocommunications referred to as LSM messages. Theygenerally indicate that a change in the state of the LSM 108 hasoccurred that is beyond the control of the LMU 106, and may be triggeredby an error condition event, a marginal condition detection, or someform of manual (e.g., door open) or diagnostic (e.g., LSM disable)event.

Specific forms of LSM commands will now be considered. One form ofcommands comprise configure and initialize commands such as the receiveddown-load command, initialize LSM command, and request LSM configurationcommand. The receive down-load command requests the LSM 108 to receiveinformation down-loaded from the LMU 106 in packets of fixed size. Apacket ID will include information specifying whether the packet istargeted for code or data memory as well as the address associated withthe packet. An option is also provided for immediate execution, startingat a specified address, or acknowledgement without execution. Thiscommand may be executed only when the LSM 108 is totally idle. Theinitialize LSM command requests the LSM 108 to initialize the electricaland mechanical portion of the LSM 108 not initialized before thefunctional code down-load. This command can only be executed if the LSM108 has been placed off-line. Initialization ending status will indicateif the LSM 108 is working properly, working in an impaired state, orunable to function. Since cartridges may have been present in either orboth hands, an indication is needed of whether or not cartridges werestored. Also, any errors that may have occurred during initializationare returned.

The request LSM configuration command requests the LSM 108 to transmitits configuration to the LMU 106. The information returned describes thephysical layout of the LSM 108. Each panel description will define thetype of panel (i.e., full-cell panel, port panel, door panel, drivepanel, etc.). This command may be issued at any time after the LSM 108has been initialized.

There are five basic commands relating to the motion of the arm assemblyportion 138 and hand-and-finger assembly 236. These commands arereferred to as arm-and-hand-motion commands, and are comprised generallyof a move-arm-only command; move, read, and get command; move-and-putcommand; move-and-read VOLSER command; and go-home command.

The move-arm-only command requests the LSM 108 to move the arm assemblyportion 138 from its current location to the "destination location." Thedestination location is a specified storage cell 132, cartridge accessport cell, port or drive. As part of the move-arm-only command, a movein the direction having 103 values will be specified. That is, themovement direction of the arm assembly portion 138 will be clockwise,counterclockwise, or LSM select best path.

The move, read, and get command requests the LSM 108 to move to aspecified location, read the volser of the cartridge 286, extend thespecified hand-and-finger assembly 236, and grasp the cartridge 286 atthat location. The LSM 108 must make provision for the type of storageunit (e.g., cell drive port) to which it has moved. After the cartridge286 has been grasped, the hand and finger assembly 236 will retract toits normal moving position.

The move-and-put command requests the LSM 108 to move to a specifiedlocation, extend the specified hand and finger assembly 236, and releasethe cartridge 286 it is currently holding. The LSM 108 must makeprovision for the type of storage unit (i.e., cell, drive, port) towhich it has moved. After the cartridge 286 has been released, thehand-and-finger assembly 236 will retract to its normal moving position.

The move-and-read VOLSER command requests the LSM 108 to move to aspecified location and read the volser at that location. The LSM 108must make provision for the type of storage unit (i.e. cell, drive port)to which it has moved. The status of the read (e.g. no cartridge, goodread, partial read, or bad read) and the VOLSER will be returned to theLMU 106.

The go-home command requests the LSM 108 to return the arm assemblyportion 138 with hand-and-finger assembly to their "home" positions. Anoption will force the LSM 108 to unwrap the cable. Ending status willreflect that either, or both, contain cartridges. This command willnormally be issued to the LSM 108 following a period in which the arm isidle. Once this command has been issued, the LSM 108 is free to executeinternal diagnostics and/or recalibrations, during the period of timeallotted to this command. Command and response with reasons for rejectsand errors are illustrated for each of the above-describedarm-and-hand-motion commands in FIGS. 43a-43e.

The cartridge access port is also commanded by the LMU 106. Cartridgeaccess port commands include generally an unlock CAP door command, lockCAP door command and a set CAP mode command. The unlocked CAP doorcommand tells the LSM 108 to unlock the cartridge access port door inthe addressed LSM 108 so that operator may open it. It also indicatesthat all CAP door opening and closing events should be reported asmessages to the LMU 102. When the CAP door is closed, the door isautomatically locked and can only be opened if the CAP is in an enter oreject mode.

The set CAP mode command tells the LSM 108 which mode the cartridgeaccess port is currently in. The cartridge access port may be in anenter mode, eject mode, or idle mode. In enter mode, cartridges 286 maybe migrated into the LSM 108. In the eject mode, cartridges 286 may beremoved through the cartridge access port. In the idle mode, thecartridge access port door will be locked and no operator access ispermitted. The LSM 108 require knowledge of the cartridge access portstatus so that it may be posted on its operator panel.

Communication flow for the above-described cartridge access portcommands is illustrated in FIGS. 44a and 44b.

Referring now to FIG. 45, there is shown the data flow of commands andresponses with their associated potential rejects and errors forpass-through port commands. The only command required for the pass-toreport is the rotate-pass-through-port command which instructs the LSM108 to rotate the specified pass-through port 180°. The pass-throughport, when not rotating, should be in one of two positions (i.e., "0" or"1") within either of its connected LSMS 108. The desired position afterthe rotation will be included as part of the command, which may beexecuted at any time.

A reset-door-open-indicator command causes the LSM 108 to reset themechanism which indicates that the access door has been opened. Such amechanism may be suitably comprised of a solenoid-operated flip-flop.

Two types of tape drive commands are relayed to the tape drive 150through the LSM 108. A rewind and unload drive command requests the LSM108 to notify a tape drive 150 that it is to rewind and unload. The LSM108 will respond to this command when the drive has become unloaded andis ready for dismount. If the drive is unloaded, or is already in theprocess of unloading, the LSM 108 will not reject the command, but willsimply respond as soon as the tape drive 150 is ready for dismounting.The second tape drive command, a request time until unloaded, requeststhe LSM 108 to notify the LMU 106 of the expected time that will elapsebefore a specified drive 150 is unloaded. If the drive 150 contains analready unloaded cartridge, the time will be zero.

Various other commands are utilized to monitor or change the status of aLSM 108. A request LSM state command requests the LSM 104 to transmitits current state or some specified part of it. The "LSM machine state"is defined by the information return. A subset of the full informationpacket can be retrieved by including the "information desired specifier"this command may be executed at any time, and is illustrated in FIG. 46.Two types of LSM varying commands are issued to change the status of theLSM 108. A vary LSM on line/off line command is issued to an LSM 108 tovary the LSM on line or off line. The LSM 108 may only be placed on linewhen it has had its functional code down loaded, has been initialized,and has been configured. When no command is active, the LSM 108 may beplaced off line. The LSM 108 must also be placed off line prior torunning off line diagnostics or opening the access to work. A vary LSMmaintenance on/off command 1.. is issued to the LSM 108 to varymaintenance mode on or off. The functional code in this case must beloaded.

Several forms of messages from the LSM 108 to the LMU 106 may beutilized in accordance with the present invention to provide LSM statusinformation or to request an action of the LMU 106 required by the LSM108. An error condition message will be issued by the LSM 108 when anyfailure occurs and will be in addition to any failing ending statuswhich might be generated for a specific command. The error message willinclude as much isolation information as the LSM 108 can ascertain.Further diagnostics may be necessary at this juncture to isolate thefailure to a single field replaceable unit.

A door opened/closed message indicates that the operator access door tothe LSM 108 has been opened or closed. Opening the door will cause allpower to be removed from the moving parts of the LSM 108. A CAP dooropened/closed message indicates that the CAP has been opened or closed.An IPL complete message indicates that the LSM 108 is ready forinitialization.

A LSM request to go home message indicates that the LSM 108 wishes toreturn the arm, wrist, and hands to their "home" positions. This requestwill eventually be honored by the LMU 106, at which time a "go home"command will be issued. An enter/eject cancelled message indicates thata CAP lock command has overridden an active ENTER or EJECT.

A LSM request code packet message indicates the LSM wants the LMU 106 todown-load either a specified packet of LSM code or the entire code. Thismessage will be transmitted to the LMU 106 when the integrity of anyportion of the LSM code becomes suspect. The LSM 108 will request a fulldown-load of all packets whenever an initiate program load is generated.The LMU 108 will acknowledge the message and issue a "receive down mode"command sequence to transmit the desired code packet, such command,being issued only when all outstanding advance to the LSM 108 have beencompleted. Whenever the LSM 108 has a change in status, a status changemessage is transmitted and will include the specific reason for thechange.

Communications initiated from the LMU 106 to the LSM 108 include thefollowing diagnostic functions. On line diagnostic, or those interleavedwith host requests to an online LSM 108, are initiated at the LMU 106the diagnostic system user such as a field engineer. Generally, thediagnostic system executing at the LMU 106 is responsible for limitingthe types of diagnostics available to the user and, therefore,protecting the LSM 108 from requests which might upset subsystemintegrity. This occurs since there is no distinction between host anddiagnostic generated LSM commands.

While on line, the LSM 108 will not be requested to perform any otherthan functional-type operations. Furthermore, if on line, the diagnosticsystem will not request LSM initialization. Typical operations in thisnote include motions which support diagnostics upon an neighboringmaintenance mode LSM such as diagnostic cartridge motion, pass throughport motion/examination, etc.. Status requests will also be issued. Aswith any of the other operating modes, an on line LSM 108 can receive acommunications port message through the conventional RS-232 port.

There are no diagnostic commands permitted in the LSM off line state. Assuch, the diagnostic of the LMU 106 may issue any functional commandallowed in the off line state such as request state or vary tomaintenance. All other commands will be rejected.

Maintenance mode diagnostics permits the LMU 106 the most comprehensivecontrol of LSM 108. In addition to all functional commands, specializeddiagnostic commands are accepted. These -, commands may disturb theintegrity of the LSM 108 such that an initialized command is requiredprior to returning to the off line state. This is known to the LMU 106via the initialized required flag contained in status which is theresponse to a request state command or the unsolicited status changemessage generated when maintenance mode is released by the user.

Finally, a diagnostic down-load command instructs the LCU 154 to accepta down-load of a diagnostic code segment. Several segments may berequired to complete a down-load, each requiring transmission of thiscommand. Each packet is identified by a segment number which indicateswhere it is to be loaded in the diagnostic buffer. The length of thecode/data segment cannot exceed a segment's capacity. Once thediagnostic code has been placed in the buffer, controlled will be passedto that code if the execution flag is set. This command may only beexecuted when the LSM 108 has been placed in maintenance mode.

Software related to the operation of the ACS 100 according to thepresent invention will now be described. Generally speaking, there arethree basic types of software required to implement the ACS 100: (1)host resident software or host software component 110, (2) LMU software,and (3) LSM software.

The host software component 110 performs as the interface between theMVS system or host computer 102, requesting tape processing, and the ACS100, performing tape mount/disk mount operations. Host software isdistributed in both system modification program/extended (SMP/E) andsystem modification program/for (SMP/4) formats. Software installationis the process of receiving, applying, and accepting the new functionsystem modification (SYS MOD) and user modification (USER MOD) whichrepresent the host software component 110. The user must then LIBGEN(i.e., the process of defining the configuration of the library to thehost software) the host software component 110 with user selectableparameters. LIBGEN outputs include an initialized control data set andlistings indicated what has been generated. Two other facilities areprovided, and installation verification process (IVP) and areconfiguration utility. The IVP can be executed to ensure properinstallation of the whole system, while the reconfiguration utilityprovides a means of enlarging and installation without having to losedata held in the control data set.

Software initiation deals with the process of starting the hostsoftware, and involves starting a task, via operator command,determining the parameters involved, and notifying the ACS 100 that thehost 102 has been initiated.

Job processing pertains to the activities a host computer 102 wouldperform for normal tape job processing. These include device separation,mount message, dismount message, and swap processing. Device separationis the term utilized to allocate tape drives to either library ornon-library functions. Since all tape drives 150 assigned to system maynot be under library control, the host software component 110 separatestape resources into distinct allocation groups. It is also a function ofdevice separation to insure selection of a drive 150 in the same ACS 100as the volume to be mounted, when used in multiple ACS 100 environments.

The host software component 110 also provides the capability todetermine when a library controlled volume is to be mounted on a librarycontrol drive. It maintains records of volume location and instructs theLMU 106 to mount the requested volume on the selected drive 150. Thisaction is referred to as mount processing. Scratch volumes may also berequested and the host software component 110 provides lowering of therequested volume from within the same LSM 108 (or nearby LSM 108 whenneeded). This action is referred to as scratch processing.

The host software component additionally provides the capability todetermine when a library controlled line is to be dismounted andreturned to its home position. Such functioning is referred to asdismount processing. Swap processing, on the other hand, is activated bythe need to remove a volume from one tape drive 150 and move it toanother drive 150. This action can be initiated by the operator, issuinga swap command, or when the operating system detects an error on aparticular drive 150 and determines the need to move the volume toanother drive 150.

Operator command to the host software component 106 are generallydivided into two groups known as library command and system commands.Library commands are provided specifically to allow an operator toprepare library resources for maintenance, to determine the status oflibrary components, and to locate a volume within the library. Ten basiclibrary commands are provided in accordance with the present invention.

VARY STATION ON LINE/OFF LINE

CAP PREFERENCE

RECOVER HOST

MODIFY LSM ON LINE/OFF LINE

DISPLAY

LIBRARY MOUNT

LIBRARY DISMOUNT

ENTER

DRAIN

EJECT

A station is defined as the connection between a host computer 102 andan LMU 106. Each host computer 102 can have one or more stations to eachLMU 106. And each LMU 106 can include stations for one to sixteen hostcomputers 102. The operator can issue a VARY STATION ON LINE/OFF LINEcommand to vary the state of each station as on line or off line to thehost computer 102 on which the command was issued. An optional parameteris provided to force the off line state immediately.

The CAP PREFERENCE command is issued by the operator to assign apreference priority for each cartridge access in the library. Higherpriority cartridge access ports are chosen over lower priority cartridgeaccess ports whenever the system chooses a particular cartridge accessport. Priorities should be assigned to minimize operator inconveniencefor cartridge access ports chosen by the system.

Under the RECOVER HOST command, the operator can have one host computer102 recover library resources assigned to a crashed host computer 102.Normal operations require a host computer 102 to obtain libraryresources to automate cartridge handling. A host computer 102 may crashwhile owning library resources, therefore, the command causes ownershipof those resources to be transferred to an operational host computer 102executing this command.

The operator can issue the MODIFY LSM ON LINE/OFF LINE command to varythe state of each LSM on line or off line to all hosts regardless towhich the command was issued. The option to force the off line stateimmediately is also provided. This command differs from others is thatit affects connection to all host computers 102 rather than just thecomputer 102 to which the command was issued.

The operator can also issue a DISPLAY command to display information asto component status of the ACS 100, location of particular volumes, andlibrary associated messages. The LIBRARY MOUNT command allows theoperator to cause the library to mount a volume or particular cartridge286 on a tape drive 150. In a similar manner, the LIBRARY DISMOUNTcommand permits the operator to dismount a volume or cartridge 286 fromthe tape drive 150.

The ENTER command is issued by the operator to effect the transfer ofcartridges 286 from the cartridge port to the LSM 108. The option ofentering multiple or single volumes is provided until a DRAIN command isissued. Under such conditions, the DRAIN command is issued to terminatethe transfer of cartridges from the cartridge access port to the LSM 108initiated by the enter command. Finally, an EJECT command can be issuedto effect the transfer of cartridges 286 from the LSM 108 to thecartridge access port. The option of ejecting multiple or single volumesor cartridges 286 is also provided.

System commands are comprised generally of three types. These providethe operator the capability to start and terminate software processing.It should be noted at this juncture that job processing, MVS commandalteration, and library commands only work while the host softwarecomponent 110 is in operation. A START command is issued by the operatorto cause the host software component 110 to start to function on aparticular host computer 102. A SHUT DOWN command, on the other hand, isissued by the operator to terminate all library processing on a hostcomputer 102. No new functions will be started by the host softwarecomponent 110. When all current functions have been completed, anycontrol data sets open will be closed and the host software component110 will cease to function. In addition, a CANCEL command provides thecapability to immediately terminate all processing and perform a dump.

Various utility programs are provided to aid the user in managinglibrary resources. For manual removal of a volume or cartridge 286, aVOLSER to location utility program is provided to determine the locationof the cartridge 286 when the operating system is not functioning. Thisallows the user to locate volumes that are required to make theoperating system functional (e.g., retrieve the SYSRES backups).

A user with a tape management system often has a data base describingwhich tapes are scratch and which are not. The data base of necessity isperiodically updated to indicate new scratch tapes. A scratch updateutility program is provided that can use the information provided fromthe user's tape management system to update the library's list ofscratched tapes. Such program can either add new scratch tapes to theexisting list or, recreate the whole scratch list from the inputprovided by the tape management system. An eject cartridge utilityprogram is also provided which can eject cartridges by accepting a listand effecting the ejection of those cartridges indicated.

A backup utility program may be provided to allow an installation totake complete and accurate backups of the control dataset. Optionally,if journaling is enabled, the journal is reset. This program executeswith or without a functioning host software component 110. The controldata set may be recreated from a previous backup copy and optionallyapplying the current journal through use of restore utility programwhich also executes with or without functioning host software component110. Finally, an audit utility program is provided to generate aphysical inventory of the entire library, and ACS 100 within thelibrary, any given LSM 108 within a specified ACS 100, or a suitablecombination of such elements. Under such circumstances, the control datasets are updated to reflect all observed changes in cell storage for thespecified only.

Log processing is the function of storing data about events to permitlater analysis and tracking of those events. As such, errors detected bythe host software component 110 are placed in SYS1.LOGREC. The hostsoftware component 110 will not handle errors normally handle errorsnormally handled by the operating system, such as drive and control uniterrors. Errors not normally handled by the operating system are loggedby the host software component 110. Additionally, the host softwarecomponent 110 will cause the logging of software failures in the errorlog. Records will be logged by MVS for each abnormal termination of thehost software component 110. All recovery actions taken by the hostsoftware component 110 will be logged in the error log to provide anaudit trail for recovery.

The primary recovery responsibility of the host software component 110is to maintain the consistency of the controlled data sets. Such setsmust correctly describe the state of the library at any given time andbe recoverable to that time. A secondary responsibility of the hostsoftware component 110 is the detection, notification of, and recoveryfrom library failures. These include loss of a host computer 102 in amultiple host computer complex, loss of one or both processors in theLMU 106, and so forth. The third area of responsibility of the hostsoftware component 110 is to work with the LMU 106 in order to recoverLSM 108 after it has failed. In particular, this includes determiningthat there are volumes or cartridges 286 in the hand and fingerassemblies 236, the pass through port, or elsewhere, discovering theirVOLSER number, and disposing of them properly.

Common functions are those that can be envoked from several of thefunctions previously described. For example, the mounting of a volume orcartridge 286 is a function activated by job processing, operator mountcommand, or a utility program among others. Any additional processingrequired by specific (non common) functions is described herein below.The host software component must determine that a volume or cartridgeneeds to be mounted on a drive 150. If the mount involves a volume orcartridge 286 under library control, or a drive 150 attached to thelibrary, the host software component 110 needs to take appropriateaction. Dismount processing must also be determined by the host softwarecomponent 110. That is, the host software component will determine thata volume or cartridge needs to be dismounted from a drive 150. If thedismount involves a drive attached to the library, the softwarecomponent needs to take appropriate action.

The host software component 110 will also cause a volume, under commonenter processing, to be entered into the library, thus placing thevolume under library control. This may involve entering volumes with noexternal specification of the volser. The host software component 110selects a "home" location for the cartridge 286 at enter time, with suchselection being performed without user control. Finally, the hostsoftware component 110 will cause the LMU 106 to scan the cells of 132of an LSM 108 to determine its contents. Audit processing can be envokedfor a single LSM 108, a single ACS 100, or the entire library comprisedof multiple ACSs 100. The audit uses the OCR label on a tape cartridge286 to specify the VOLSER. Any tape cartridge with no OCR label or witha defective OCR label will be ejected from the ACS 100. Such cartridges286 require manual verification of volume serial numbers prior toreentry into an ACS 100.

In order to increase the efficiency of the mounting process, the hostsoftware component 110 influences allocation of a drive 150 closest tothe cell 132 in which a volume of cartridge 286 resides. Causingallocation to favor the closest drive 150 is called directed allocation.When a job's data set allocation requests a library controlled volume,directed allocation attempts to cause the closest available drive 150 tobe allocated to the job. Directed allocation only pertains to volumesand drives under library control and excludes tape resources outside thelibrary.

When a user needs to enter an LSM 108 to manually remove a volume orcartridge 286, a VOLSER to location utility is provided to generate areport that lists the location of volumes within the library. Thelocation must be in a format that allows the user to locate a volume. Asan alternative, the user can use the library display command todetermine the location of a volume. The volume's location willsubsequently be displayed with mount messages when the system operates,in manual mode.

In order to allow the user to better utilize the library, an activitydistribution utility program is provided that can generate a reportshowing relative activity by LSM 108 and/or by VOLSER. The user can thenredistribute resources to balance the load. A scratch redistributionutility program is also provided to allow the user to redistribute andbalance the number of scratch volumes per LSM 108 of an ACS 100. Thisprogram accepts an ACS ID and performs a redistribution of volumeswithin the specified ACS 100. Concurrent redistribution may beaccomplished by multiple executions of the scratch redistributionutility program.

In order to allow the entering of nonlabeled tape cartridges 286 for thepurposes of labeling, an initialize new cartridge utility program isalso provided. This utility places a cartridge access port into"initialization mode". All entered cartridges 286 will be initialized tomatch their OCR label. The user can then specify the newly initializedcartridges should be ejected from the library or entered into the poolof scratch volumes. The cartridge access port will continue toinitialize volumes until empty.

System management facility records will be created in accordance withthe present invention for library events which affect the utilization ofhost software component 110 resources, for events which indicatecartridge insertion or deletion, and for performance data from the LMU106/LSM 108. Information recorded in system management facility filesthus better aid the user to manage his library resources.

As discussed herein above, the host software component 110 is capable ofrunning on any host computer 102 that supports a IBM MVS/XA operatingsystem, and must operate in a multi-host computer 102 environment withup to 16 host computers 102 sharing the library. All host computers 102using a particular library share the same control files or control dataset. Therefore, a given host computer 102 may be connected to only onelibrary.

Since the ACS 100 according to the present invention may includenon-library attached tape transports 150, the host software component110 attempts to influence allocations such that non-library volumes donot get allocated to library attach drives 150, and library volumes donot get allocated to non-library attached drives.

The host software component 110 is supported by IBM MVS/XA only. Assuch, the host software component 110 provides a user exit to replaceany user exits taken by itself. As much common code and data above the16 megabyte line as possible is attempted to be maintained by the hostsoftware component 106. Common code and data refers to code or datashared among all address groups. No modification to the IBM code isnecessary.

The JES2 portion of MVS/XA is not supported by the host softwarecomponent 110 since JES2 does not require automated tape services. Theonly tape related function of JES2 is set up, which tells the operatorto release the job when the specified volumes are available. However,JES2 does not request the operative to mount the volumes. The hostsoftware component 106, on the other hand, must be able to support theJES3 portion of MVS/XA, including having library tape resources set upand broken down by JES3. Additionally, the host software component 110supports RACF, without compromise to its integrity. In addition, allutilities issue calls to RACF (if active) to determine if the job/useris authorized to envoke that utility. Usage of library control tapetransports 150 as controlled by a hierarchical storage manager is alsosupportive by the host software component 110 through dynamic allocationof the tape drives 150.

Third party software is not explicitly provided support by the hostsoftware component 110. However, the host software component 110supports conventional tape managing products known as Tape ManagementSystem (TMS) and Tape Library Management System (TLMS), using itsknowledge of TMS and TLMS to determine the scratch status of libraryvolumes. For other more customized tape management systems, the hostsoftware component 110 provides a documented interface to its scratchroutine. As a result, the user must provide the interface routinebetween the tape management system and the scratch routine of the hostsoftware component 110. The host software component 110 will not supportmultiple scratch pools. Only requests for VOLSERS with "PRIVAT" orSCRTCH will be considered as requests for scratch volumes. If the volumechosen by the host software component 110 fails to satisfy the mountrequest, the operator is required to resolve the situation.

For correct operation of the library system, the host software component110 must be operating on all host computers 102 which can allocatelibrary volumes. By doing this, the host software component 110 is ableto monitor requests for library volumes from non-library hosts, andrequests operator intervention.

For JES2 shared spooled complexes, the host software component 106 needonly be active on host computers 102 which have access to librarycontrolled tape transports 150. This assumes that the host softwarecomponent 110 will not perform JCL converter or interpreter processing,i.e., there will be no "SUBSYS=" clause on library tape DD statements.Correct operation can only be guaranteed for a JES3 complex if the hostsoftware component 110 executes on the global processor of JES 3, aswell as all local processors capable of performing tape drive set up. Inaddition, the constraints which apply to JES2 shared spool complexesapply here as well.

With reference now to FIGS. 47-49, the LMU software utilized for controlof the ACS 100 will be described. On power up, the LMU 106 is controlledby software located in read only memory having two goals. That is, toverify that the processor and its immediate environment are working wellenough to attempt the initial program load from mass storage, and toload LMU functional software as described in detail herein below fromthe mass storage device into random access memory and give it programcontrol. The initial hardware checkout is of a "go/no go", nature. Ifthe checkout fails, the failure indication must be easy to see and havea simple interface that has a high degree of reliability although muchof the LMU 106 is not operating. This program, as a result, initializes,tests, and verifies the operation of the processor, the ROM, the ROMused for the initial software load, timers, interrupts, and the massstorage device.

Once the "go/no go" tests referred to above have been completed, initialsoftware is loaded into the RAM by reading blocks of data from the massstorage device. The software, which is loaded, contains more extensivehardware check out routines and a secondary software loading program.Software loaded during the initial program load checks the fullfunctionality of the LMU 106 including detection of non-fatal errors, aswell as no go condition. This includes testing of hardware previouslychecked, plus initialization and testing of utility RS-232 interface,host interfaces, LSM interfaces, and the operating panel interface. OnceLMU hardware operation has been verified, the entire functional softwarepackage as illustrated in FIG. 49 can be loaded from mass storage intoRAM and control is passed from hardware initialization to softwareinitialization.

The LMU system software consists of two major components: (1) thecontrol program, and (2) the LMU functional software. The controlprogram provides for the overall management of the individual tasks ofthe LMU functional software. Each LMU task is self-contained (i.e., onetask does not directly control or call any other task). By using systemcalls, the tasks are able to communicate and coordinate with othertasks. The control program also provides a central point of control ofthe hardware contained in the LMU 106.

In a presently preferred embodiment of the invention, the controlprogram is a multi-tasking control program (MTCP) microprocessor 518.The MTCP is embedded for such application, and supplies multi-taskingsupport, interrupt driven, priority based scheduling, intertaskcommunication and synchronization, dynamic memory allocation, real timeclock control, and real time responsiveness. The control programsupports interfaces to LMU tasks and hardware through one of threemeans: (1) basic MTCP system calls, (2) LMU extended systems calls, and(3) interrupt routine as shown in FIG. 47. LMU extended system calls areextensions to the MTCP that primarily provide tasks with the ability tointerface with the LMU hardware. These input/output system calls are thecentral point of controlling hardware for the LMU functional software asshown in FIG. 49. Interrupt routines provide LMU specific handling ofhardware interrupt, and are conceptionally a part of the controlprogram, not a part of user tasks. The primary function of the interruptroutines is to interpret the interrupt, perform any necessary hardwareinput/output, and notify the appropriate task of pending work, if any.Interrupts work outside the normal MTCP scheduling control and theiractivity is kept to a minimum.

At bring-up time, the LMU functional software requires initialization.At such time, it is assumed that only the control program isoperational. The initialization, described below, brings the various LMUfunctional software tasks into existence. Also at bring-up, all queuesused for task communication and all static tasks (i.e., tasks that. Allrequired memory partitions are created at initialization using the"create memory partition" system call.

Tasks in the LMU functional software are comprised of either statictasks or dynamic tasks. Static tasks are created at initialization andare never deleted. They are dedicated to continually performing aspecific function. Dynamic tasks, on the other hand, are created upondemand, exist until a task is completed, and then deleted. Each hostrequest received creates a task for the duration of that host request.This allows the control program to manage multiple host requests of thesame type. The system calls "task create" and "task delete" are used forthe creation and deletion of tasks, respectively.

The MTCP allows each task to execute independently with each task havingno direct control over any other. Communication type MTP system callsallow a task to: (1) send messages to other tasks, and (2) receivemessages from other tasks. The two basic means of communication providedby the MTCP are mailboxes and message queues.

In general, tasks remain suspended from execution until the task has aneed to run. Tasks in the LMU functional software are designed to waitupon the occurrence of a single event, multiple events from one source,or multiple messages from multiple queues. A task can wait until singleevent occurs by using the system calls "pend for message" and "postmessage". By convention, several tasks agree to use a common mailbox ormemory location for communication. A waiting task issues the "pend formessage" system call to a particular mailbox. The task is suspendeduntil the event is signalled by another task. When another task issuesthe "post message" system call to the common mailbox, the waiting taskthen becomes available for execution. This is the simplest form ofinter-task communication.

A task can also wait on multiple events being communicated to it via asingle message queue. The systems calls "pend for message from queue"and "post message to queue" are used in this scenario. By using thesystem call "pend for queue message", a task becomes suspended fromexecution for as long as the queue remains empty. Other tasks can thensend multiple messages to the single queue by the system call "postmessage to queue". With the queue now having messages, the MTCPeventually resumes execution of the waiting task. After the firstmessage is handled, the task again issues system call "pend for messagefrom queue". If the MTCP determines another message is on the queue, andno other task has higher priority, the task will be given control again.If the task does not get immediate control back to process the nextqueue message, the task still remains ready to execute but will not bedispatched until later. If the queue is empty when the system call "pendfor message from queue" issued, the task is suspended by the MTCP.

Many of the tasks in the LMU 106 must wait on multiple messages frommultiple queues. This function is not directly supported by the MTCP andhence is implemented using a combination of system calls.

The waiting task tries to accept messages from all its queues. If any isfound it is processed and the check is repeated. If none is found thetask pends on the common mailbox. The sender posts a message to thedesired queue and then posts it to the common mailbox. The message inthe mailbox reactivates the pending task which then accepts messagesfrom each of its queues until it finds one.

As described hereinabove, the control program provides the central pointof controlling the LMU hardware. All LMU tasks use system calls whenthey need to request some activity of the hardware. Such system callsinclude "get time of day", and "set time of day". As shown in FIG. 48,these task initiated system calls are represented by "call XXXX". Thecontrol program takes this system call and manipulates the hardware toaccomplish the request. Generally, a return code is returned to the taskindicating completion status. The means by which the hardware notifies atask of them occurs differently from that of the task initiatedinput/output. Referring again to FIG. 48, the hardware interrupt thecontrol program. If this interrupt requires a task to be notified, thesystem call "post to queue from interrupt handler" is used to post aspecific message to the appropriate task's queue. At a later time, thereceiving task will then process a message.

Interrupt routines are conceptionally a part of the control program.However, when an interrupt occurs, it is invoked outside the normal flowof task scheduling. The function of interrupt routines is to interpretthe interrupt, notify the appropriate task of any work required (usingthe "post from interrupt handler" system call), manipulating necessaryhardware controls, and exiting (using the "exit from interrupt handler"system call). The "exit from interrupt handler" system call causesrescheduling to occur, if any higher priority task became ready toexecute as a result of the interrupt processing.

The LMU functional software relies on the control program to manage usermemory for all variable data. The basic partitions of memory areestablished at initialization using the "create memory partition" systemcall. In order to make optimum use of memory, the LMU functionalsoftware uses dynamic allocation of memory. A task, when it needsmemory, issues a "get memory block" system call to obtain the neededmemory. When the task no longer needs the memory, the "release memoryblock" system call is issued releasing the memory for other use.

When any task issues the "get memory block" system call, it has thepotential for being rejected due to memory being unavailable. The meansof avoiding this error is described in greater detail hereinbelow, butif it occurs, the task issues the "task delay" system call to retry thememory request at a later time. If the task continually fails to obtainmemory, the current request is aborted. A rejection message is sent toany waiting task. The "post message to queue" system call can berejected if the receiving queue is full, and is recovered using the sametechnique described hereinabove with reference to memory errors.

Time outs are needed for those tasks requiring a completion messagewithin a certain amount of time. When a task initially sends a messageto another task, it obtains a time-stamp with the "time" system call.When each task is suspended with the "pend for message from queue"system call, a time out is specified. This particular time out causesthe task to be scheduled even if no other normal work is required.Either by the pend time out value or normal scheduling, the task will bedispatched. The task will then examine each of its outstanding items fora time out. Recovery of each time out is dependent on the specific task.

As discussed hereinabove, the utilization of various resources in theLMU functional software is dynamic in nature. Such resources may becomprised generally of message queues, memory blocks, and task controlblocks. When a task reaches a resource limit, it cannot continue itsnormal execution. The recovery, as described immediately hereinabove, isnot desirable. Therefore, the following considerations will be used inan attempt to avoid resource depletion.

Each task started from the host requires a certain amount of messagequeue space, a task control block, and various memory blocks. Theprimary means of avoiding depletion of these resources is by limitingthe number of host requests that can be active at any given time. Sincereceipt of a host request causes a dynamic task to be created, the hostrequests are limited by limiting the total number of tasks. The MTCPthereafter rejects the "task create" system call when a predefined tasklimit, for example 64, is reached. The total number of task is somewhatgreater when other static tasks are included. Other considerations ofresource depletion involve controlling the scheduling between varioustasks. The overall attempt is to avoid any blank times and keep theutilization of queues and memory to a minimum.

Avoiding queue overflow is also accomplished by establishing a prioritywithin each task. Most tasks in the LMU 106 wait on multiple queues andmailboxes. For these tasks, an emphasis is placed on handling messagesthat are outbound to the host computer 102 before accepting messagesthat are inbound to the LMU 106.

In the following description, transformation definitions are includedwhere appropriate Such transformations depict the decomposition of anincoming request into a series of communications between the task beingdefined and its input and output queues and mailboxes. Referring now toFIG. 5,, there is shown an example of a dismount for the process hostrequest task. In this case, the task involves multiple LSMs 108 with thesource drive 150 and destination cell 132 being located in differentLSMs 108. The dismount command arrives at step (2) and is transformedinto the transactions listed in steps (3) through (21). The first actiontaken is the posting (3) of a rewind unload drive command to the LSMrequest queue. Since the LSM response to this command, drive unloaded(5), may not be received immediately, a path allocation request (4) isissued so that it may be processed at the same time as the unload. Thesymbols surrounding and separating steps (5) and (7) indicate thatreception of the two transmissions are independent, and that the orderof their occurrence cannot be predicted. The task pends itself to bothmailboxes and must receive both pieces of information before it cancontinue.

Once the drive 150 is unloaded and a pass-through port slot path hasbeen allocated, the actual dismount may begin. A move get command with adrive parameter is posted to the LSM request queue (a) and the taskpends to its LSM response mailbox for the move get complete response(9). When the response is received, a tape dismounted response is postedto the host response queue. Similarly, the move put to a slot (11) isposted and its response pended upon step (12). After the first slot,there may be zero or more slots to pass through in the allocated slotpath. The symbols around steps (13) and (16) indicate that there may bezero of more slot-to-slot moves.

The tape cartridge 286 must be retrieved from the final slot using themove get command with a slot parameter (17), and the response must bepended upon step (18). The final command to the LSM 108 is a move put tothe destination cell (19). Once the response for this command isreceived (20), the final host response (cell full) is posted to the hostresponse queue at step (21) and the transformation is complete.

Referring again to FIG. 49, it can be seen that the host interfacecommunications task sends and receives all data to and from the hostinterfaces. Its primary purpose is to act as a go-between for the hostinterfaces and the LMU functional software.

The host interface communications task is activated when data isavailable from a host interface. If the communication is a host request,a new copy of the task which handles that request is created. The hostrequest is then transmitted to that task. Any other communications fromthe host interfaces must be a host message reply and will be sent on tothe process host messages task. The host message replies are hostacknowledgments to previously transmitted host messages.

Host responses are also received by the host interface communicationtask from the process host request task during and on completion of ahost request. Such host responses carry status information associatedwith a specified host request. The data is subsequently transmitted tothe appropriate host interface.

From the diagnostic interface, the host interface communication taskalso accepts host type requests. It processes these requests and theresponses as it does for the host interface, except for thecommunications tasks. The process host messages task is used to post"host messages" to the host interface communications tasks. Hostmessages are communications from the LMU 106 to the host computer 102that are not related to a specific host request. Such messages aredescribed in detail hereinabove and are written to the appropriate hostinterface.

The process host request function shown in FIG. 49 is actually composedof a set of tasks, each of which handles a single type of host requestor diagnostic request. Many copies of a single task may be active at anyone time. A copy of the task is created by the host interfacecommunications task and the host request which initiated it is sent tothat task. The parameters of the request are checked, and if not valid,the request may be rejected.

If the request requires the movement of a cartridge 286 from one LSM 108to another, or movement to a drive 150, a path must be requested fromthe allocate slot path task prior to the assurance of any LSM commands.

The host request is transformed into a series of "LSM commands" whichare transmitted individually to the LSM interface communications task.Commands requiring allocatable resources (e.g., hand, arm or portmechanism) must not be issued until the allocate resource task hasgranted allocation rights for such resources. The host request taskpends itself to each "LSM response".

When a "LSM response" containing request status is received from the LSMinterface communications task, any necessary intermediate status, (e.g,"cell empty response") and/or completion status is sent to the hostcomputer 102. This is done by issuing a "host response" to the hostinterface communications task. When a response is received, thoseresources which can be released must be returned to the allocateresource task so that other tasks may have their turn.

Any error conditions are recorded in the error log. Statistics on theexecuted command are gathered when the host request is complete,communications from the process host request tasks indicating whetherthe request was initiated by the host interface or the diagnosticsinterface.

The allocate resources task is responsible for all allocatable LSMresources in the ACS 100. Such resources include port slot paths, tapedrive, LSM hands and arms, and pass-through port mechanisms. They alsoinclude entire LSMs 108 for the purpose of varying an LSM on-line,off-line or to maintenance mode.

Any host request, which needs to pass a cartridge from one LSM 108 toanother or is moving a cartridge 286 to a drive 150, must requestallocation of an entire "slot path" from this task before it can beginissuing any LSM motion requests. When a path from the source LSM 108 tothe destination LSM 108 has been selected for which there is anon-allocated pass-through port in each of the connecting pass-throughports, that path in the form of the selected slots is allocated to therequesting task. A slot remains allocated until it has been used andemptied.

If the task has requested a drive 150 as its destination location, thistask will not release a path allocation until the specified drivecontains no cartridge. The drive 150 is then considered allocated duringthe requesting task and until a dismount or swap task removes thecartridge 286 from that drive 150.

Before a task can initiate a motion command, it must receive allocationof any resources needed to complete that command. Such resources arecombinations of arms, hands, and pass-through port mechanisms. As a taskcompletes the use of any resource at the end of an LSM command, it mustrelinquish its allocation of that resource. Some resources, such as anarm, must be returned at the end of each command which needs it. Thisallows other tasks a chance to use it. Others, such as a hand, must beretained across more than one LSM command.

The allocate resources task must maintain dynamic ACS configuration. Anyresources added to this system, for example, as a LSM 108 goes on line,or removed from the system, for example, as the LSM 108 goes off line,are reported to this task by the task (i.e., host command or LSMmessage) which gets the information from the LSM 108. This task willreject resource requests initiated from host requests if the specifiedresources reside in an LSM 108 which is not on line. Similarly, requestsinitiated from diagnostic sources will be rejected unless the selectedLSM 108 is in maintenance mode.

As is the processed host request task, the process LSM messages task isactually a set of tasks, each of which handles a single type of LSMmessage. Many copies of a single task may be active at any one time. Acopy of the task is created by the LSM interface communications task,and the LSM message which initiated is sent to that task.

If the LSM message requires it, a series of "LSM commands" is createdand transmitted individually into the LSM interface communications task.Any commands requiring allocatable resources (e.g., hand, arm or portmechanisms) must not be issued until the allocate resource task penditself to each "LSM response".

An "LSM response", containing request status, is received from the LSMinterface communications task. When such a response is received, thoseresources which can be released must be returned to the allocateresources task so that other tasks can have their turn. Most errorconditions and manual intervention messages will be relayed as hostmessages to the host interface communications task. Some host messages,however, require acknowledgment from the host. But those host replieswill be received from the host interface communications task. Any errorconditions are recorded in the error log.

The LSM interface communications task sends all data to, and receivesall data from, the LSM interface comprised of LAN. Its primary purposeis to act as go-between for the LAN and the rest of the LMU functionaland diagnostic software.

The LSM interface communications task receives "LSM commands" from theprocess host requests task, the process LSM message task, or from thediagnostic interface. Commands are transmitted to the appropriate LSM108 over the LAN. When these commands are complete, LSM responses arereturned from the LSMs 108. This status is relayed back to the taskwhich initiated the LSM command.

Unsolicited communications from the LSMs 108 in the form of LSM messagesare also received on the LSM interface. When one is received, this taskcreates a new process LSM message task to handle that message. Theinitial message is then sent to the newly created task for processing.

Error handling within the ACS 100 is not centralized. It is distributedwithin the system with each portion responsible for the reporting andrecovery of any error that it detects. Retries will occur at the"lowest" possible level. The LSM 108 is responsible for all retriesinvolving a single LSM command. On the other hand, the LMU 106 willretry any portion of a host command which involves more than one LSM108, or can use an alternative path (e.g., another hand or port). Everypiece of the system is responsible for its own process recovery.Similarly, within the LMU 106, error recovery is distributed. Retriesoccur at the lowest level and each task is responsible for its ownrecovery.

A task which receives a request which is not understood or cannot beexecuted will issue a reject for that request. The rejection is returnedin place of the normal response to the request. Rejections are logged inthe error log. No recovery is possible at this level. A task whichreceives a rejection for a request may assume that the rejection hasbeen logged, but is responsible for any recovery or retry of its ownprocess. A task issues an error response for a request it receives onwhich it takes action but cannot complete. The error response isreturned in place of the normal ending response to that request. Anyerror which is detected by a task must be logged by that task. This taskis also responsible for any retry or recovery algorithm which may beappropriate. Tasks which become aware of a problem through an errorresponse, need take no action on that error but must attend to anyrecovery of their own process that is possible.

With reference now to FIGS. 51 and 52, a description of the softwarerequired for the LSM 108 will be described. On power up and afterprocessor reset, the LSM 108 will begin execution out of the read onlymemory. The role of the read only memory code is two-fold, in that itverifies that all electronic systems work and can be communicated with,and that it requests and loads the functional software from the LMU 106.The code is transmitted from the LMU 106 to the LSM 108 via the localarea network that connects the two. Once the functional code has beenloaded, it runs additional tests against the electronic hardware. Testsare run to weed out marginal hardware and to determine field replaceableunits. If such tests run with no errors, then control is turned over tothe function main (which is responsible for "waking up" the operationalsoftware).

Like the LMU software, the LSM system software is segmented into twodistinct components: a control program and the LSM functional software.The control program is responsible for controlling the flow ofoperations from the time an LMU command comes in, throughout theexecution phase and into and through the ending response phase.Different tasks that are needed to satisfy LMU demands can communicatewith the LMU and to each other through the control program. In apresently preferred embodiment of the invention, the control program isimplemented with a MTCP for multi-tasking support, interrupt driven,priority-based synchronization, intertask communication andsynchronization, direct memory allocation, real time clock control andreal time responsiveness. The MTCP system calls, used by the controlprogram, are shown in FIG. 51.

At bring-up time, the LSM functional software shown in FIG. 52 requiresinitialization, since it is assumed that only the control program isoperational. The initialization described below brings the various LSMfunctional software tasks into existence.

The LAN is first shut off to prevent the old PROM code from beingactivated and the OP₁₃ PANEL lights are initialized. The current task israised to the highest level to prevent rescheduling during theinitialization procedure. All required memory partitions are created byci₁₃ impart (), and all communication queues are created with ci₁₃ ques(). The USARTS, TIMERS and INTERRUPT chips are initialized, the servodata structures are initialized by ci₁₃ init (), and the DC₋₋ SERVOinterrupt and MTCP Timer interrupt are enabled. All of the tasks arecreated by ci₁₃ ctask (). The STATE of the machine is then set to IPL₁₃COMP (IPL Complete ) or DOOR₁₃ AJAR if the Access Door is not closed ).Since the above described operations are performed in the ci₁₃ main ()task, the only dynamic task, it deletes itself at this point.

The MTCP allows each task to execute independently with each task havingno direct control over any other. Communication type MTCP system callsallow a task to: (1) send messages to other tasks, and (2) receivemessages from other tasks. As in the LMU functional software, the twobasic means of communication provided by the MTCP are mailboxes andmessage queues.

In general, tasks remain suspended from execution until the task has aneed to run. Tasks in the LSM functional software are designed to waiton the occurrence of a single event, multiple events from one source, ormultiple messages from multiple queues. Detailed descriptions of thoseoccurrences are described with reference to task communication with theLMU functional software.

There are two forms of interrupts in the LSM 108. The first form ishidden from the MTCP but linked to other functions through the MTCP.These types of interrupts are called system interrupts, the function ofwhich is to figure out the interrupt, notify the appropriate task of anywork required (using "post from interrupt handler" system call),manipulating necessary hardware controls, and exiting (using the "exitfrom interrupt handler" system call). The "exit from interrupt handler"system call causes rescheduling to occur if any higher priority taskbecomes ready to execute as a result of the interrupt processing.

The other type of interrupt is dedicated to the servo control of amechanism or a group of mechanisms. These types of interrupts are calledservo interrupts, the function of which is to control the position ofthe particular mechanism. It communicates to the LSM functional softwareand not at all to the control program. Hence, these interrupts arehidden from the MTCP and not linked to other functions through the MTCP.They communicate through a set of servo data structures without the aidof the MTCP.

Memory management and system errors within the LSM functional softwareare identical to those described herein above with reference to the LMUfunctional software.

Referring again to FIGS. 51 and 52 wherein the LSM functionalarchitecture and functional software task processing are respectivelyshown, a description of those tasks will follow.

The LAN interface communications task, or ls₁₃ intrf(), pends on: /bx₁₃lmui/ with input from (ls₋₋ lout) and /bx₁₃ diag/. It is this function'sjob to be the interface between the LAN andtwo tasks: the DiagnosticInterface Task and the LMU Interface Communications Task. The data to besent will be in (ls₁₃ lout) or /bx₁₃ diag/ depending on what the sourceis. The filling of /bx)lmui/ signals this task that there is someinformation that it must send out to the LAN. It is responsible forputting the message on the LAN and handling all LAN error recovery. Wheninformation comes down the LAN to this LSM, an interrupt will wake upthis task and it will get the message. ACL the sender and pass theinformation onto (ls₁₃ inq). It is this task's responsibility to releasethe memory blocks that are used as input buffers.

The diagnostic interface communications task, or sp intf (), pends on(ls₁₃ dque). This task is the pathway between the diagnostic interfaceand LAN interface. Information comes from the LAN to the diagnosticinterface via (ls₁₃ dque) where the address of the buffer containing thedata is found. When information comes from the diagnostic interface, itis directed to the LAN using two mailboxes. The first mailbox /bx₁₃diag/ is where the pointer to the data goes and the second mailbox hasto be filled with any non zero data to signify that there is data in /bxdiag/. It is this task's job to handle all the communications associatedwith the Diagnostic Port.

The LMU interface communications task, or li etask (), pends on (ls₁₃inq). Since this task is the main hub of the LSM functional software,commands come into from the LAN interface task. The LMU interfacecommunications task checks certain parameters and responds to the LMU106 E₁₃ CMND in the error field and if they are all available then theyare reserved for this command. This is to prevent conflicts of resourcesbetween nonrelated commands. If a required resource is unavailable forany reasons then this function will return the correct end status backto the LAN Interface Task.

This task fills the appropriate mailbox or queue in order to start thejob that was requested. This Task then waits on (1s inq) for jobCompletion Status or for another LMU command. When the Completion statuscomes in it is passed on to the LAN Interface Task and the resource isfreed for use by another command.

The following types of commands are resource limited: (1) Passthru Portmovement commands; (2) Tape Drive commands; and (3) Functional commands.The following types of commands are NOT resource limited: (1) CartridgeAccess Port commands; and (2) Miscellaneous commands.

The LSM error and statistics, or er₁₃ task (), pends on (ie₁₃ respq).This task is responsible for keeping the local error log and statisticlog. It transforms the data in the Response Buffer into data suitablefor the LAN Interface Task. In addition, it will be monitoring the errorrate of each mechanism and when necessary, it will make a mechanisminoperative. All communications that are directed to the LMU, passthrough this task first. Only after this task has updated its logs willthe information be passed to the LMU Interface Communications Task. Ifthe response has caused a major state change, then an unsolicitedmessage will be queued up for the LMU.

The two process pass through port tasks, Process PTP 0 Task and ProcessPIP 1 Task, are identical except for the ports they control. These taskspend respectively on: /bx₁₃ ptOrq/ or /bx₁₃ ptlrq/, and are necessary tomove a Passthru Port to the requested position and to respond to the LMU106 with Ending Status.

The process CAP task, or ca₁₃ task (), pends on a cartridge access portrequest /bx₁₃ aprq/. This task is responsible for operating thecartridge access port, and generates an LMU message during cartridgeaccess port door opening and closing events, such messages being sentvia the (le₁₃ respq). The process CAP task is also the means by whichthe cartridge access port door gets locked and unlocked. The process CAPtask is also responsible for satisfying the unlock CAP door and set CAPmode LMU commands.

The process operator panel task, or op₁₃ ask (), pends on an up panel(op₁₃ ndq), is responsible for controlling the operator panel,interpreting the message and modifying the operator panel displaysaccordingly. When any key on the operator panel is pressed, an interruptwill wake up the processor operator panel task and an LMU message willbe sent up to the LAN via (1e respq). This task is responsible forhandling the access door open and closed messages, and for handling thepower off request interrupt.

The process tape drive task, or td₁₃ rqst (), pends on a tape driverequest (td-req), waiting for a command to be put into the (td₁₃ req).Any command is processed and the result of the command put in one ofthree places. If the command came from the process functional commandtask, the return information is placed into /bx₁₃ fresp/. If the commandcame from the process miscellaneous commands task, then the returninformation gets put into /bx₁₃ mresp/. On the other hand, if thecommand came from the LMU interface communications task, the informationwill be returned in (le₁₃ respq). Accordingly, the format of the commandallows for determining where the command came from. The process tapedrive task also is responsible for satisfying the rewind and unload tapedrive and request time to unload LMU commands.

This task is responsible for satisfying the following LMU Commands: (1)Rewind and Unload Tape Drive; (2) Request Time to Unload; (3) Tape Drivereset; (4) Hold off load of Tape Drive; (5) Reset hold-off-load; (6)Blank out Tape Drive display; and (7) Tape Drive sense.

The process functional commands task, or fc₁₃ prorq (), pends on afunctional command request (/bx₁₃ funrq/). Arm movement commands arereferred to as functional commands and are controlled by such tasks.When the task wakes up, it finds an arm movement command pointed to byits mailbox and completes the movement. If the movement involves thetape drive, this function will send a command to the tape drive via(td₁₃ eq). It then pends on /bx fresp/ for the information it wants andcontinues with its job. When the movement is completed, it sends endingstatus via (1e respq). The process functional commands task also isresponsible for satisfying the following LMU commands:

INITIALIZE LSM

MOVE ARM ONLY

MOVE, READ AND GET

MOVE AND PUT

MOVE AND READ VOLSER

GO HOME

VARY LSM ON LINE/OFF LINE

VARY LSM MAINTENANCE MODE ON/OFF

DIAGNOSTIC DOWN LOAD

The process no activity time out task, or pn₋₋ noact (), ends on an armin use /bx₁₃ armus/. When an arm movement is finished, the processfunctional commands task referred to above puts the current time in/bx-armus/ and signifies that it just finished a move. Thereafter, theprocess no activity time out task is awakened by that event and will putitself to sleep pending on the same mailbox but with a time out. Themailbox will be filled again whenever arm activity is initiated. If thetask times out while the arm is idol, the arm has not been used duringthe time out. It will then send a message to the LM 106 requesting thatthe arm be allowed to go home and unwind. The communications path to theLMU 106 is via (le₁₃ respq).

The process miscellaneous commands task, or mi₁₃ task (), pends on amiscellaneous commands request /bx₁₃ misrq/, and wakes up when a commandis sent to its mailbox. The command is interpreted by the task andprocess, with ending status being returned via RESP. This task isresponsible for satisfying the following LMU commands:

RECEIVE DOWN LOAD

REQUEST LSM CONFIGURATION

RESET DOOR OPEN INDICATOR

REQUEST LSM STATE

Unlike the above described tasks, the environmental monitoring task doesnot pend on any mailbox or queue. It puts itself to sleep for a specificamount of time, and when it wakes up, it checks power supply voltagesand various temperatures of the machine parts. If anything is out ofspecification, it will post an error code to the LSM error andstatistics task, sending a message to the LMU. Software data flow forthe LSM 108 is shown in FIGS. 53a, 53b, and 53c.

All error recovery from mechanical movements is contained in the LSM108. If the LSM 108 tells the LMU 106 it could not fulfill a command, itcan be assumed that it cannot be done. The LMU 106 should not resubmitthe command since the LSM 108 did everything it could do to perform itthe first time.

The LMU functional software must be cognizant of its performance whenmotion is in progress. In the event of a failure in a mechanism'smovement, the software must automatically retry the motion. Eachmechanism will have its own retry ability coded into the movementfunctions. If that fails, the higher level movement functions willenvoke retries on multiple mechanisms in order to complete the job. Ifthat in turn fails, then the job cannot be done and ending status willreflect the failure to complete the job.

While a particular embodiment of the invention has been shown anddescribed, various modifications are within the true spirit and scope ofthe invention. The appended claims are, therefore, intended to coversuch modifications. ##SPC1##

What is claimed is:
 1. In a data processing system, a storage andretrieval subsystem comprising:a plurality of magnetic tape cartridges,each of said plurality of magnetic tape cartridges being adapted to havedata written thereto and read therefrom; a host computer; library meansfor storing said plurality of magnetic tape cartridges in substantiallyupright positions, said library means including a first cylindricalarray of storage cells centered about a vertical axis and a secondcylindrical array concentrically arranged about said first array; alibrary tape unit including a plurality of tape drives, each of saidtape drives being adapted to receive one of said plurality of magnetictape cartridges in a substantially horizontal transducing position;robotic means for transferring said plurality of magnetic tapecartridges between their substantially upright storage positions and thesubstantially horizontal transducing positions at said plurality of tapedrives; outboard controller means adapted to receive commands from saidhost computer for interfacing between said host computer and saidlibrary means; and inboard controller means, within said library means,adapted to receive commands form said outboard controller means forinterfacing between said outboard controller means and said roboticmeans.
 2. A storage and retrieval subsystem according to claim 1,wherein said robotic means comprises:a support column centered on saidvertical axis; an arm assembly rotatably mounted upon said supportcolumn, said arm assembly being adapted for rotation about said verticalaxis; a wrist assembly mounted at the distal end of said arm assemblybetween said first and second arrays; and means, coupled between saidarm assembly and said wrist assembly, for moving said wrist assemblyvertically with respect to said arm assembly.
 3. A storage and retrievalsubsystem according to claim 2, wherein said robotic means furthercomprises a vision system that is operatively coupled to said inboardcontroller means, said vision system being adapted to feedbackinformation to said inboard controller means regarding a position ofsaid robotic means relative to a preselected storage cell.
 4. A storageand retrieval subsystem according to claim 3, wherein said vision systemcomprises:a pair of video cameras adapted to read encoded means foridentifying each said magnetic tape cartridge, each said magnetic tapecartridge having a unique one of said identifying means affixed thereto;and interface logic and memory means, operatively coupled between saidwrist assembly and said inboard controller means, for fine positioningif said wrist assembly to said preselected storage cell.
 5. A storageand retrieval subsystem according to claim 2, wherein said wristassembly comprises:a turntable; and a pair of hand assemblies mountedupon said turntable in opposing relationship, both of said pair of handassemblies including a gripper assembly adapted to grasp saidcartridges.
 6. A storage and retrieval subsystem according to claim 5,wherein said gripper assembly further comprises means for rotating saidcartridges between their substantially upright storage positions and thesubstantially horizontal transducing positions.
 7. A storage andretrieval subsystem according to claim 2, wherein said robotic meansfurther comprises a remote electronics interface mounted on said armassembly and operatively coupled to said inboard controller means forcontrolling said robotic means.
 8. A storage and retrieval subsystemaccording to claim 1, wherein said library means further comprises meansfor manually inputting and outputting a plurality of said cartridges. 9.A storage and retrieval subsystem according to claim 8, wherein saidmanual input/output means comprises:a cartridge access port mountedwithin and adapted to open outwardly from said second array; a thirdarray of storage cells attached to said cartridge access port; and meansattached to said cartridge access port and said second array, forpreventing access to said first and second arrays when said cartridgeaccess port is open to said third array, said access preventing meanswhen said cartridge access port is open covering said opening in saidsecond array.
 10. A storage and retrieval subsystem according to claim1, further comprising:means, coupled to an outer portion of said librarymeans, for transferring a plurality of said cartridges remotely fromsaid first and second arrays.
 11. An improved storage and retrievalsubsystem in a data processing system having a host computer and aplurality of tape transports coupled for communication with the hostcomputer, each of the tape transports being adapted for use withmagnetic tape cartridges, wherein the improvement in combinationtherewith comprises:a first array of storage cells, each of said cellsconsisting essentially of a back portion and bottom portion separatingtwo side portions, and an open front portion adapted for insertion ofone of the magnetic tape cartridges, wherein said cells are radiallydisposed about a vertical axis with their respective front portionsinwardly directed thereto; structural means for supporting said firstarray, said structure means including a floor portion, ceiling portion,and a segmented wall portion substantially surrounding said first array;a second array of storage cells, an upper portion thereof beingsuspended from said ceiling portion and a lower portion thereof mountedon said floor portion wherein an open path is defined there between,said upper and lower portions having their cells radially disposed aboutsaid vertical axis, concentrically inward from said first array, withtheir respective front portions outwardly directed therefrom; a robotmounted for rotation about said vertical axis, said robot includingmeans for transferring the cartridges between said cells and the tapetransports; and means adapted to receive commands from the host computerfor interfacing between the host computer and said robot.
 12. Theimprovement according to claim 11, wherein said robot comprises:asupport column mounted upon said floor portion; a theta arm rotatablymounted upon said support column, said theta arm being adapted to rotatehorizontally within the open path defined between said upper and lowerportions; and means for rotating said theta arm.
 13. The improvementaccording to claim 12, wherein said transfer means comprises:a turntableadapted for movement between said first and second arrays; a pair ofhand assemblies mounted in an opposed relationship upon said turntable;and means, attached to the distal end of said theta arm, for moving saidturntable vertically with respect to said theta arm.
 14. The improvementaccording to claim 13, wherein each of said hand assembliescomprise:gripper means for holding one of the cartridges; means forextending and retracting said gripper means; and means for rotating saidgripper means about its axis of extension and retraction.
 15. Theimprovement according to claim 14, wherein said gripper meanscomprises:a pair of fingers; toggle means coupled to said pair offingers for opening and closing same; a lead screw coupled to saidtoggle means; a nut threadedly coupled to said lead screw; and motormeans rigidly coupled to said nut in order to rotate same therebycausing said lead screw to move towards or away from said toggle meansand opening or closing same.
 16. The improvement according to claim 14,wherein said extension and retraction means comprises:a pair of rodsslidingly supporting said gripper means upon a plurality of rollerbearings; a lead screw; a nut threadedly coupled to said lead screw andrigidly attached to said gripper means; motor means attached to saidlead screw for rotating same thereby causing said nut and said grippermeans to move along its axis of extension and retraction.
 17. Theimprovement according to claim 14, wherein said rotating meanscomprises:a motor; a first gear attached to said motor; and a secondgear, larger than said first gear and coupled thereto by a belt, saidsecond gear being attached to said hand assembly to rotate same.
 18. Amethod of storage and retrieval of data contained in a plurality ofmagnetic tape cartridges, comprising:forming a first cylindrical arrayof storage cells centered about a vertical axis, said first arraycomprising an upper and a lower portion; forming a second cylindricalarray of storage cells concentrically arranged about said first array;rotatably deploying robotic means for picking and placing said pluralityof magnetic tape cartridges from and to said first and second arrays;providing a plurality of tape drives adapted to receive said magnetictape cartridges from said robotic means; and interfacing said first andsecond arrays, robotic means, and tape drives for maximizing access by ahost computer to the data stored in said magnetic tape cartridges. 19.The method according to claim 18, wherein said forming steps furthercomprise orienting said storage cells for maintenance of said magnetictape cartridges in substantially upright positions therein.
 20. Themethod according to claim 18, wherein said step forming said secondarray comprises:suspending said upper portion; and mounting said lowerportion beneath said suspended upper portion; wherein said suspendedupper portion and said mounted lower portion form an access path therebetween.
 21. The method according to claim 20, wherein said deployingstep comprises:providing a support column at the vertical axis; couplingone end a rotatable arm to said support column for rotation within saidaccess path; and coupling to the other end of said rotatable arm a pairof hand and finger assemblies.
 22. The method according to claim 21,further comprising:supporting said pair of hand and finger assembliesupon a turntable; and providing means for raising and lowering saidturntable.
 23. The method according to claim 22, wherein said supportingstep comprises mounting said pair of hand and finger assemblies in anopposing relationship upon said turntable.
 24. The method according toclaim 23, wherein said forming step of said second array includesforming a portion thereof for manually inputting a plurality of saidcartridges, said portion being adapted for access by said hand andfinger assemblies.
 25. The method according to claim 24, furthercomprising:(a) manually inputting a plurality of said cartridges in saidportion of said second array; (b) retrieving a selected one of theplurality of cartridges with said robotic means; (c) selecting one ofsaid storage cells for storing said cartridge; (d) rotating said roboticmeans with said retrieved cartridges from said manual input portion tosaid selected storage cells; (e) placing said cartridge in its selectedcell; (f) rotating said robotic means back to said manual input portion;and (g) repeating steps (b) through (f).
 26. The method according toclaim 25, wherein said retrieving step comprises:extending one of saidhand and finger assemblies to said manual input portion; gripping saidselected cartridge; and retracting said hand and finger assembly withsaid selected cartridge.
 27. An automated method of retrieving datacontained in a plurality of magnetic tape cartridges, comprising:storingsaid plurality of magnetic tape cartridges in a library having an outercylindrical array of cells and an inner cylindrical array of cells, saidouter array being radially inwardly disposed and said inner array beingradially outwardly disposed; forming an access path between said outerand inner arrays; controlling a robot having six degrees of freedomwithin said access path for selectively picking and placing saidcartridges; and coupling at least one tape drive adapted for use withmagnetic tape cartridges with said library.
 28. The method according toclaim 27, further comprising:selecting a cartridge stored in apredetermined cell; rotating said robot within said access path to afirst position corresponding radially to said predetermined cell; movingsaid robot vertically within said access path to a second positioncorresponding to the elevation of said predetermined cell; extendingsaid robot to a third position proximate to said selected cartridge;gripping said selected cartridge with said robot; retracting said robotwith said gripped cartridge to said second position; moving said robotwith said gripped cartridge to a fourth position within said accesspath, said fourth position corresponding to the elevation of said tapedrive; and extending said robot with said gripped cartridge to a loadingposition within said tape drive.
 29. The method according to claim 27,wherein said coupling step comprises providing a cartridge trayrotatably mounted upon said tape drive for movement from an inclinedloading position to a substantially horizontal transducing position. 30.The method according to claim 27, wherein said storing step furthercomprises arranging said cells to store said cartridges in asubstantially upright position.